U.S. patent number 10,815,910 [Application Number 16/450,704] was granted by the patent office on 2020-10-27 for control device for compression ignition engine.
This patent grant is currently assigned to Mazda Motor Corporation. The grantee listed for this patent is Mazda Motor Corporation. Invention is credited to Masayoshi Higashio, Michio Ito, Yuta Masuda, Yuto Matsushima, Yugou Sunagare, Kenko Ujihara.
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United States Patent |
10,815,910 |
Masuda , et al. |
October 27, 2020 |
Control device for compression ignition engine
Abstract
A control system for a compression ignition engine is provided,
which includes a sensor and a cylinder count control module which
changes between all-cylinder and reduced-cylinder operations when
the compression ignition combustion is performed at a given lean
air-fuel ratio. The cylinder count control module executes a
preparation control to change from the all-cylinder operation to
the reduced-cylinder operation when the change is demanded. In the
preparation control, the cylinder count control module outputs a
signal to a throttle valve to execute an air amount increase
processing, outputs a signal to a fuel injection valve to execute a
fuel amount increase processing, and outputs a signal to an
ignition plug to execute a retard processing. The cylinder count
control module ends the fuel amount increase processing and the
retard processing when it is determined that an air-fuel ratio is
in a given air-fuel ratio state, and starts the reduced-cylinder
operation.
Inventors: |
Masuda; Yuta (Hiroshima,
JP), Higashio; Masayoshi (Hiroshima, JP),
Sunagare; Yugou (Hiroshima, JP), Ito; Michio
(Hatsukaichi, JP), Ujihara; Kenko (Higashihiroshima,
JP), Matsushima; Yuto (Hatsukaichi, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mazda Motor Corporation |
Aki-gun, Hiroshima |
N/A |
JP |
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Assignee: |
Mazda Motor Corporation
(Aki-gun, Hiroshima, JP)
|
Family
ID: |
1000005141591 |
Appl.
No.: |
16/450,704 |
Filed: |
June 24, 2019 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20200032720 A1 |
Jan 30, 2020 |
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Foreign Application Priority Data
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Jul 26, 2018 [JP] |
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2018-140637 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D
41/3017 (20130101); F02D 17/02 (20130101); F02B
31/06 (20130101); F02D 41/0002 (20130101); F02P
5/15 (20130101); F02D 13/0203 (20130101); F02P
5/045 (20130101); F02D 41/38 (20130101) |
Current International
Class: |
F02D
41/30 (20060101); F02D 41/38 (20060101); F02B
31/06 (20060101); F02D 17/02 (20060101); F02D
41/00 (20060101); F02D 13/02 (20060101); F02P
5/04 (20060101); F02P 5/15 (20060101) |
Field of
Search: |
;123/481,198F,198DB,198DC,399,406.45 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1707791 |
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Oct 2006 |
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EP |
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3418538 |
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Dec 2018 |
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EP |
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2018096744 |
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May 2018 |
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WO |
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Other References
European Patent Office, Extended European Search Report Issued in
Application No. 19186906.4, dated Dec. 9, 2019, Germany, 11 pages.
cited by applicant.
|
Primary Examiner: Huynh; Hai H
Attorney, Agent or Firm: Alleman Hall Creasman & Tuttle
LLP
Claims
What is claimed is:
1. A control device for a compression ignition engine, the engine
comprising: a plurality of cylinders; pistons configured to
reciprocate inside the plurality of cylinders, respectively; a
plurality of combustion chambers, each defined in the cylinders so
that displacement of the combustion chamber changes according to
the reciprocation of the piston; a throttle valve configured to
adjust an amount of air supplied into each of the combustion
chambers; ignition plugs disposed so as to be oriented to the
respective combustion chambers; and fuel injection valves
configured to inject fuel into the respective combustion chambers,
the control device comprising circuitry and a sensor configured to
measure a parameter relevant to an operation of the engine, wherein
the control device is configured to execute a cylinder count
control module connected with the throttle valve, the ignition
plugs, the fuel injection valves, and the sensor, to output signals
to the throttle valve, the ignition plug, and the fuel injection
valves based on the signal inputted from the sensor so that a
compression ignition combustion is started by the ignition plug
igniting a mixture gas formed by the fuel injection valves
injecting fuel into each of the combustion chambers, and configured
to change between an all-cylinder operation in which combustion is
performed in all of the plurality of combustion chambers and a
reduced-cylinder operation in which combustion is not performed in
some of the combustion chambers by suspending the fuel injection
into the combustion chambers, according to an operating state of
the engine, when the compression ignition combustion is performed
at a given lean air-fuel ratio higher than a stoichiometric air
fuel ratio, wherein the cylinder count control module executes a
preparation control to change the operation of the engine from the
all-cylinder operation to the reduced-cylinder operation when a
change demand from the all-cylinder operation to the
reduced-cylinder operation is received, and wherein in the
preparation control to change the operation of the engine from the
all-cylinder operation to the reduced-cylinder operation: the
cylinder count control module outputs the signal to the throttle
valve to execute an air amount increase processing in which an
amount of air supplied to each of the combustion chambers is
increased during the change of the operation of the engine from the
all-cylinder operation to the reduced-cylinder operation, compared
with the amount of air before the preparation control is started,
the cylinder count control module outputs the signal to the fuel
injection valves to execute a fuel amount increase processing in
which an amount of fuel injected into each of the combustion
chambers is increased during the change of the operation of the
engine from the all-cylinder operation to the reduced-cylinder
operation, compared with the amount of fuel before the preparation
control is started, the cylinder count control module outputs the
signal to the ignition plug to execute a retard processing in which
an ignition timing is retarded, and the cylinder count control
module ends the fuel amount increase processing and the retard
processing when the cylinder count control module determines that
an air-fuel ratio is in a given air-fuel ratio state where the air
amount reaches a given amount, and starts the reduced-cylinder
operation.
2. The control device of claim 1, wherein the air-fuel ratio state
is determined when the cylinder count control module determines
that a rich air-fuel ratio defined based on the amount of air, and
the amount of fuel injected in the reduced-cylinder operation
during the change, reaches a given threshold.
3. The control device of claim 2, wherein the threshold is a value
lower than the lean air-fuel ratio.
4. The control device of claim 1, wherein a restricted retard
processing in which the ignition timing is restricted below a
retarding amount at that time is performed after the retard
processing reaches a limit.
5. The control device of claim 4, wherein a load adjustment
processing in which a part of output of the engine is diverted to
some other purposes is performed, in addition to the restricted
retard processing.
6. The control device of claim 1, wherein the control device stores
a given all-cylinder operating range and a given reduced-cylinder
operating range, and wherein when the operating state of the engine
is determined to be within the reduced-cylinder operating range,
the control device performs the reduced-cylinder operation by
suspending the fuel injection by the fuel injection valves of some
of the cylinders, and opening and closing of intake valves and
exhaust valves of the cylinders are permitted during the
reduced-cylinder operation.
7. The control device of claim 1, wherein the control device
determines an actual amount of air in each of the combustion
chambers; the control device calculates a rich limit torque based
on the actual amount of air in each of the combustion chambers, the
rich limit torque obtained when combustion is performed when the
cylinder count control module determines that the air-fuel ratio is
in the given air-fuel ratio state where the air amount reaches the
given amount; the control device determines whether the rich limit
torque is below a target torque that is configured based on a
signal from an accelerator opening sensor; when the rich limit
torque is below the target torque, the control device repeatedly
executes the air amount increase processing, the fuel amount
increase processing, and the retard processing of the preparation
control until the rich limit torque exceeds the target torque; and
when the rich limit torque exceeds the target torque, then the
control device shifts the operation of the engine to the
reduced-cylinder operation.
8. A control device for a compression ignition engine, the engine
comprising: a plurality of cylinders; pistons configured to
reciprocate inside the plurality of cylinders, respectively; a
plurality of combustion chambers, each defined in the cylinders so
that displacement of the combustion chamber changes according to
the reciprocation of the piston; a throttle valve configured to
adjust an amount of air supplied into each of the combustion
chambers; ignition plugs disposed so as to be oriented to the
respective combustion chambers; and fuel injection valves
configured to inject fuel into the respective combustion chambers,
the control device comprising circuitry and a sensor configured to
measure a parameter relevant to an operation of the engine, wherein
the control device is configured to execute a cylinder count
control module connected with the throttle valve, the ignition
plug, the fuel injection valves, and the sensor, to output signals
to the throttle valve, the ignition plug, and the fuel injection
valves based on the signal inputted from the sensor so that a
compression ignition combustion is started by the ignition plug
igniting a mixture gas formed by the fuel injection valves
injecting fuel into each of the combustion chambers, and configured
to change between an all-cylinder operation in which combustion is
performed in all of the plurality of combustion chambers and a
reduced-cylinder operation in which combustion is not performed in
some of the combustion chambers by suspending the fuel injection
into the combustion chambers, according to an operating state of
the engine, when the compression ignition combustion is performed
at a given lean air-fuel ratio higher than a stoichiometric air
fuel ratio, wherein the cylinder count control module executes a
preparation control to change the operation of the engine from the
reduced-cylinder operation to the all-cylinder operation when a
change demand from the reduced-cylinder operation to the
all-cylinder operation is received, wherein in the preparation
control to change the operation of the engine from the
reduced-cylinder operation to the all-cylinder operation: the
cylinder count control module outputs the signal to the throttle
valve to execute an air amount decrease processing in which an
amount of air supplied to each of the combustion chambers is
decreased during the change the operation of the engine from the
reduced-cylinder operation to the all-cylinder operation, compared
with the amount of air before the preparation control is started,
the cylinder count control module outputs the signal to the fuel
injection valve to execute a fuel amount maintain processing in
which an amount of fuel injected into each of the combustion
chambers is maintained during the change the operation of the
engine from the reduced-cylinder operation to the all-cylinder
operation, and the cylinder count control module ends the fuel
amount maintain processing when the cylinder count control module
determines that an air-fuel ratio is in a given air-fuel ratio
state where the air amount reaches a given amount, and starts the
all-cylinder operation, wherein the control device determines an
actual amount of air in each of the combustion chambers; wherein
the control device calculates a rich limit torque based on the
actual amount of air in each of the combustion chambers, the rich
limit torque obtained when combustion is performed when the
cylinder count control module determines that the air-fuel ratio is
in the given air-fuel ratio state where the air amount reaches the
given amount; wherein the control device determines whether the
rich limit torque is below a target torque that is configured based
on a signal from an accelerator opening sensor; wherein when the
rich limit torque is below the target torque, the control device
repeatedly executes the air amount decrease processing and the fuel
amount maintain processing of the preparation control until the
rich limit torque exceeds the target torque, and wherein when the
rich limit torque exceeds the target torque, then the control
device shifts the operation of the engine to the all-cylinder
operation.
9. The control device of claim 8, wherein the control device stores
a given all-cylinder operating range and a given reduced-cylinder
operating range, and wherein when the operating state of the engine
is determined to be within the reduced-cylinder operating range,
the control device performs the reduced-cylinder operation by
suspending the fuel injection by the fuel injection valves of some
of the cylinders, and opening and closing of intake valves and
exhaust valves of the cylinders are permitted during the
reduced-cylinder operation.
Description
TECHNICAL FIELD
The disclosed technology relates to a control device for a
compression ignition engine.
BACKGROUND OF THE DISCLOSURE
It is known that combustion by compressed self-ignition in which a
mixture gas combusts at once without flame propagation being
intervened maximizes fuel efficiency because of the shortest
combustion period. However, various problems of the combustion by
compressed self-ignition need to be solved to be applied to
automobile engines. For example, since the operating state and the
environmental condition vary largely in the automotive application,
it is a large problem to carry out a stable compressed
self-ignition. In the automobile engines, the combustion by
compressed self-ignition has not yet put in practical use.
In order to solve this problem, for example, WO2018/096744A1
proposes SPCCI (SPark Controlled Compression Ignition) combustion
in which SI (Spark Ignition) combustion and CI (Compression
Ignition) combustion are combined. SI combustion is combustion
accompanied by the flame propagation started by forcibly igniting
the mixture gas inside a combustion chamber. CI combustion is
combustion started by compression ignition of the mixture gas
inside the combustion chamber. SPCCI combustion is combustion in
which the mixture gas inside the combustion chamber is forcibly
ignited to start the combustion by flame propagation, and unburnt
mixture gas inside the combustion chamber then combusts by
compression ignition due to a pressure buildup caused by generation
of heat and flame propagation of the SI combustion. Since SPCCI
combustion includes the CI combustion, it is one form of
"combustion by compression-ignition."
CI combustion in SPCCI combustion takes place when the in-cylinder
temperature reaches the ignition temperature which is defined by
the composition of the mixture gas. Fuel efficiency can be
maximized if the in-cylinder temperature reaches the ignition
temperature near a compression top dead center and CI combustion
takes place. The in-cylinder temperature increases according to an
increase in the in-cylinder pressure. The in-cylinder pressure
during SPCCI combustion is a result of two pressure buildups
comprised of a pressure buildup by a compression work of a piston
during a compression stroke and a pressure buildup caused by the
generation of heat during the SI combustion.
Since SPCCI combustion is one form of compression ignition
combustion, stable combustion is possible even if the air-fuel
ratio of the mixture gas is made leaner than a stoichiometric air
fuel ratio, as also disclosed in WO2018/096744A1. The engine which
performs SPCCI combustion can be operated at high thermal
efficiency, while suppressing the generation of raw NO.sub.x by
making the air-fuel ratio of the mixture gas 25:1 or higher.
When such an engine operates in an operating range at a low load,
since the fuel amount is little, the air-fuel ratio becomes
excessively lean and the stable CI combustion may become difficult.
Therefore, the present inventors considered that fuel injections
are stopped in some of a plurality of combustion chambers where
combustion is performed (a so-called "fuel cutoff") to change the
operation from an all-cylinder operation in which all the
combustion chambers perform combustion to a reduced-cylinder
operation in which only some of the combustion chambers perform
combustion.
However, in such a case, the air amount and the fuel amount are
different greatly between the all-cylinder operation and the
reduced-cylinder operation. Thus, the air amount and the fuel
amount have to be changed according to the respective operations,
while reducing fluctuations of torque (torque shock). In that case,
there is a problem such that raw NO.sub.x is generated or the
combustion becomes unstable.
For example, when changing from the all-cylinder operation to the
reduced-cylinder operation, the number of combustion chambers where
combustion is performed decreases. Thus, in order to reduce the
torque fluctuations while maintaining the total amount of fuel
supplied to the engine, it is necessary to relatively increase the
fuel amount supplied to the combustion chambers where combustion is
performed, and the total amount of air supplied to the engine also
have to be increased accordingly.
Regarding the increase in air, it takes place with a delay with
respect to the increase in fuel because of the structural reasons.
Therefore, if the operation is changed instantly, the air-fuel
ratio of the mixture gas increases immediately to generate raw
NO.sub.x. On the other hand, if a certain change period (a
preparation period) is provided and the operation is changed after
the increase in air, raw NO.sub.x will not be generated, but the
stable SPCCI combustion becomes difficult because the air-fuel
ratio becomes excessively leaner.
On the contrary, when changing from the reduced-cylinder operation
to the all-cylinder operation, the number of combustion chambers
where combustion is performed increases. Therefore, in order to
reduce the torque fluctuations while maintaining the total amount
of fuel supplied to the engine, it is necessary to relatively
decrease the fuel amount supplied to each combustion chamber, and
the total amount of air supplied to the engine must also be
decreased accordingly.
Therefore, in this case, if the operation is changed instantly, the
air-fuel ratio of the mixture gas becomes excessively lean and the
stable SPCCI combustion becomes difficult. On the other hand, if
the certain change period (preparation period) is provided and the
operation is changed after the reduction in air, raw NO.sub.x will
be generated.
SUMMARY OF THE DISCLOSURE
Therefore, one purpose of the technology disclosed herein is to
provide a control device for an engine which performs given
compression ignition combustion at a lean air-fuel ratio, which is
capable of smoothly changing an engine operation between an
all-cylinder operation and a reduced-cylinder operation, while
preventing a degradation of an emission performance of the
engine.
According to one aspect of the present disclosure, a control device
for a compression ignition engine is provided. The engine includes
a plurality of cylinders, pistons configured to reciprocate inside
the plurality of cylinders, respectively, a plurality of combustion
chambers, each defined in the cylinder so that displacement of the
combustion chamber changes according to the reciprocation of the
piston, a throttle valve configured to adjust an amount of air
supplied into each of the combustion chambers, ignition plugs
disposed so as to be oriented to the respective combustion
chambers, and fuel injection valves configured to inject fuel into
the respective combustion chambers.
The control device includes circuitry and a sensor configured to
measure a parameter relevant to operation of the engine, and the
control device is configured to execute a cylinder count control
module connected with the throttle valve, the ignition plug, the
fuel injection valve, and the sensor, to output signals to the
throttle valve, the ignition plug, and the fuel injection valve
based on the signal inputted from the sensor so that the
compression ignition combustion is started by the ignition plug
igniting a mixture gas formed by the fuel injection valve injecting
fuel into each of the combustion chambers, and configured to change
between an all-cylinder operation in which combustion is performed
in all of the plurality of combustion chambers and a
reduced-cylinder operation in which combustion is not performed in
some of the combustion chambers by suspending the fuel injection
into the combustion chambers, according to an operating state of
the engine, when the compression ignition combustion is performed
at a given lean air-fuel ratio higher than a stoichiometric air
fuel ratio.
Note that the number of the combustion chambers is not limited, and
depends on the specification of the engine. Similarly, the number
of the combustion chambers concerning the reduced-cylinder
operation is not limited. The lean air-fuel ratio used herein is,
for example, 25:1 or higher.
The cylinder count control module executes a preparation control to
change operation of the engine from the all-cylinder operation to
the reduced-cylinder operation when a change demand from the
all-cylinder operation to the reduced-cylinder operation is
received. In the preparation control, the cylinder count control
module outputs the signal to the throttle valve to execute an air
amount increase processing in which an amount of air supplied to
each of the combustion chambers is increased, compared with the
amount of air before the preparation control is started, the
cylinder count control module outputs the signal to the fuel
injection valve to execute a fuel amount increase processing in
which an amount of fuel injected into each of the combustion
chambers is increased, compared with the amount of fuel before the
preparation control is started, the cylinder count control module
outputs the signal to the ignition plug to execute a retard
processing in which the ignition timing is retarded, and the
cylinder count control module ends the fuel amount increase
processing and the retard processing when the cylinder count
control module determines that an air-fuel ratio is in a given
air-fuel ratio state where the air amount reaches a given amount,
and starts the reduced-cylinder operation.
That is, in such a control device for the compression ignition
engine, when changing from the all-cylinder operation to the
reduced-cylinder operation, this change is performed by executing a
given preparation control, not changing instantly. Therefore, the
air amount or the fuel amount does not change suddenly.
Moreover, in the preparation control of the control device, the
fuel amount increase processing in which the fuel amount is
increased and the retard processing in which the ignition timing is
retarded are executed in addition to the air amount increase
processing in which the air amount is increased. Since the fuel is
increased together with the air, both of the air amount and the
fuel amount approach the condition of the reduced-cylinder
operation. Thus, a smooth change is possible. Since the change in
the air-fuel ratio also becomes small, a stable combustion or
suppression of raw NO.sub.x can be achieved.
If the fuel amount is increased, generally the torque outputted
from the engine changes. In this regard, according to the control
device in which the retard processing is executed, the torque can
be kept constant, i.e., the fluctuation of the torque can be
avoided.
Moreover, if the operation is changed under a state where the air
amount is insufficient, the air-fuel ratio becomes rich and raw
NO.sub.x may be generated. Whereas, if the operation is changed
under a state where the air amount is excessive, the air-fuel ratio
becomes excessively lean and the combustion may be unstable.
In this regard, according to the control device, the fuel amount
increase processing and the retard processing are ended when the
air-fuel ratio is in the given air-fuel ratio state where the air
amount reaches the given amount which is neither excess nor
deficiency, and starts the reduced-cylinder operation. Thus, the
operation can be changed smoothly, while preventing degradation of
emission performance.
According to another aspect of the present disclosure, a control
device for a compression ignition engine is provided. The engine
includes a plurality of cylinders, pistons configured to
reciprocate inside the plurality of cylinders, respectively, a
plurality of combustion chambers, each defined in the cylinder so
that displacement of the combustion chamber changes according to
the reciprocation of the piston, a throttle valve configured to
adjust an amount of air supplied into each of the combustion
chambers, ignition plugs disposed so as to be oriented to the
respective combustion chambers, and fuel injection valves
configured to inject fuel into the respective combustion chambers.
The control device includes circuitry and a sensor configured to
measure a parameter relevant to operation of the engine, and is the
controld device is configured to execute a cylinder count control
module connected with the throttle valve, the ignition plugs, the
fuel injection valves, and the sensor, to output signals to the
throttle valve, the ignition plug, and the fuel injection valve
based on the signal inputted from the sensor so that the
compression ignition combustion is started by the ignition plug
igniting a mixture gas formed by the fuel injection valve injecting
fuel into each of the combustion chambers, and configured to change
between an all-cylinder operation in which combustion is performed
in all of the plurality of combustion chambers and a
reduced-cylinder operation in which combustion is not performed in
some of the combustion chambers by suspending the fuel injection
into the combustion chambers, according to an operating state of
the engine, when the compression ignition combustion is performed
at a given lean air-fuel ratio higher than a stoichiometric air
fuel ratio. The cylinder count control module executes a
preparation control to change operation of the engine from the
all-cylinder operation to the reduced-cylinder operation when a
change demand from the all-cylinder operation to the
reduced-cylinder operation is received. In the preparation control,
the cylinder count control module outputs the signal to the
throttle valve to execute an air amount increase processing in
which an amount of air supplied to each of the combustion chambers
is increased, compared with the amount of air before the
preparation control is started, the cylinder count control module
outputs the signal to the fuel injection valve to execute a fuel
amount maintain processing in which an amount of fuel injected into
each of the combustion chambers is maintained, and the cylinder
count control module ends the fuel amount maintain processing when
the cylinder count control module determines that an air-fuel ratio
is in a given air-fuel ratio state where the air amount reaches a
given amount, and starts the reduced-cylinder operation.
In the preparation control of the control device, while the air
amount is increased, the fuel amount is maintained without being
increased. Thus, the air-fuel ratio becomes lean, and if the
control is continued, the combustion becomes unstable.
In this regard, according to the control device, the fuel amount
maintain processing is ended when the air-fuel ratio is in the
given air-fuel ratio state with the air-fuel ratio which is neither
excess nor deficiency, and starts the reduced-cylinder operation.
Thus, the operation can be changed smoothly, while preventing the
degradation of an emission performance.
According to still another aspect of the present disclosure, a
control device for a compression ignition engine is provided. The
engine includes a plurality of cylinders, pistons configured to
reciprocate inside the plurality of cylinders, respectively, a
plurality of combustion chambers, each defined in the cylinder so
that displacement of the combustion chamber changes according to
the reciprocation of the piston, a throttle valve configured to
adjust an amount of air supplied into each of the combustion
chambers, ignition plugs disposed so as to be oriented to the
respective combustion chambers, and fuel injection valves
configured to inject fuel into the respective combustion chambers.
The control device includes circuitry and a sensor configured to
measure a parameter relevant to operation of the engine, and the
control device is configured to execute a cylinder count control
module connected with the throttle valve, the ignition plug, the
fuel injection valve, and the sensor, to output signals to the
throttle valve, the ignition plug, and the fuel injection valve
based on the signal inputted from the sensor so that the
compression ignition combustion is started by the ignition plug
igniting a mixture gas formed by the fuel injection valve injecting
fuel into each of the combustion chambers, and configured to change
between an all-cylinder operation in which combustion is performed
in all of the plurality of combustion chambers and a
reduced-cylinder operation in which combustion is not performed in
some of the combustion chambers by suspending the fuel injection
into the combustion chambers, according to an operating state of
the engine, when the compression ignition combustion is performed
at a given lean air-fuel ratio higher than a stoichiometric air
fuel ratio. The cylinder count control module executes a
preparation control to change operation of the engine from the
reduced-cylinder operation to the all-cylinder operation when a
change demand from the reduced-cylinder operation to the
all-cylinder operation is received. In the preparation control, the
cylinder count control module outputs the signal to the throttle
valve to execute an air amount decrease processing in which an
amount of air supplied to each of the combustion chambers is
decreased, compared with the amount of air before the preparation
control is started, the cylinder count control module outputs the
signal to the fuel injection valve to execute a fuel amount
maintain processing in which an amount of fuel injected into each
of the combustion chambers is maintained, and the cylinder count
control module ends the fuel amount maintain processing when the
cylinder count control module determines that an air-fuel ratio is
in a given air-fuel ratio state where the air amount reaches a
given amount, and starts the all-cylinder operation.
This control device executes the preparation control to change
operation of the engine from the reduced-cylinder operation to the
all-cylinder operation when the change demand from the
reduced-cylinder operation to the all-cylinder operation is
received, which is contrary to the control device described above.
In such a preparation control, while the air amount is decreased,
the fuel amount is maintained without being decreased.
Thus, the air-fuel ratio becomes rich, and if the control is
continued, raw NO.sub.x may be generated.
In this regard, according to this control device, the fuel amount
maintain processing is ended when the air-fuel ratio is in the
given air-fuel ratio state with the air-fuel ratio neither excess
nor deficiency, and starts the all-cylinder operation. Thus, the
operation can be changed smoothly, while preventing the degradation
of an emission performance.
The air-fuel ratio state may be determined when the cylinder count
control module determines that a rich air-fuel ratio defined based
on the amount of air, and the amount of fuel injected in the
reduced-cylinder operation during the change, reaches a given
threshold.
In a case where the total amount of fuel supplied to the engine
during the change is maintained substantially constant in order to
reduce the torque fluctuations, the fuel amount injected into the
combustion chambers in which the combustion is performed in the
reduced-cylinder operation becomes larger than the fuel amount
injected into the corresponding combustion chambers in the
all-cylinder operation. Thus, the air-fuel ratio during the change
becomes relatively rich. Therefore, by determining that such an
air-fuel ratio during the change (rich air-fuel ratio) reaches the
given threshold and by determining the air-fuel ratio state as a
reference of the change timing, the change can be possible at an
early stage while suppressing raw NO.sub.x.
The threshold may be a value lower than the lean air-fuel
ratio.
The lean air-fuel ratio is higher than the stoichiometric air-fuel
ratio. Thus, if the fuel amount increases relative to the air
amount, it may be the air-fuel ratio at which raw NO.sub.x is
generated. Therefore, the threshold is set to a suitable rich value
lower than the lean air-fuel ratio and, thus, the operation can be
changed at the limit before generating raw NO.sub.x.
Therefore, the suppression of raw NO.sub.x is possible while
securing the combustion stability more reliably.
A restricted retard processing in which an ignition timing is
restricted below a retarding amount at that time may be performed
after the retard processing reaches the limit.
After the retard processing reaches the limit, if the ignition
timing is further retarded, a misfire may occur. Therefore, by
restricting the ignition timing below the retarding amount when the
retard processing reaches the limit, the misfire caused by the
retard processing can be avoided.
A load adjustment processing in which a part of output of the
engine is diverted to some other purposes may be performed, in
addition to the restricted retard processing.
In a state where the restricted retard processing is executed, if
the fuel is continued to be increased, the torque increases and the
torque fluctuation may occur. In this regard, according to this
control device, since the part of output of the engine is diverted,
i.e., used for another purpose different from the generation of the
torque, the increase of the fuel amount can be continued while
reducing the torque fluctuation even after the retard processing
reaches the limit.
The control device may store a given all-cylinder operating range
and a given reduced-cylinder operating range. When the operating
state of the engine is determined to be within the reduced-cylinder
operating range, the control device may perform the
reduced-cylinder operation by suspending the fuel injection by the
fuel injection valves of some of the cylinders, and opening and
closing of intake valves and exhaust valves of the cylinders may be
permitted during the reduced-cylinder operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view illustrating a configuration of an engine.
FIG. 2 is a view illustrating a configuration of a combustion
chamber, where an upper portion corresponds to a plan view of the
combustion chamber, and a lower portion is a cross-sectional view
taken along a line II-II.
FIG. 3 is a plan view illustrating a configuration of the
combustion chamber and an intake system.
FIG. 4 is a block diagram illustrating a configuration of an engine
control device.
FIG. 5 is a graph illustrating a waveform of SPCCI combustion.
FIG. 6 is a view illustrating maps of the engine, where the top is
a map when the engine is warm, the middle is a map when the engine
is half-warm, and the bottom is a map when the engine is cold.
FIG. 7 is a view illustrating details of the map when the engine is
warm.
FIG. 8 is a view illustrating a layer structure of the maps of the
engine.
FIG. 9 is a flowchart illustrating a control process according to a
layer selection of the maps.
FIG. 10 is a flowchart illustrating a control process related to a
change between a reduced-cylinder operation and an all-cylinder
operation.
FIG. 11 is a graph illustrating a relation between a generated
amount of raw NO.sub.x and A/F during combustion.
FIG. 12 is a flowchart illustrating a basic control of the
engine.
FIG. 13 is a block diagram illustrating a functional block of an
ECU related to the change between the reduced-cylinder operation
and the all-cylinder operation.
FIG. 14 is a flowchart illustrating a first preparation control
pattern related to a change from the reduced-cylinder operation to
the all-cylinder operation.
FIG. 15 is a view illustrating a calculation procedure at the
retard limit torque.
FIG. 16 is a view illustrating a calculation procedure at the rich
limit torque.
FIG. 17 is a time chart illustrating the first preparation control
pattern.
FIG. 18 is a flowchart illustrating a second preparation control
pattern related to the change from the reduced-cylinder operation
to the all-cylinder operation.
FIG. 19 is a time chart illustrating the second preparation control
pattern.
FIG. 20 is a flowchart illustrating a third preparation control
pattern related to a change from the all-cylinder operation to the
reduced-cylinder operation.
FIG. 21 is a time chart illustrating the third preparation control
pattern.
DETAILED DESCRIPTION OF THE DISCLOSURE
Hereinafter, one embodiment of the disclosed technology will be
described in detail with reference to the accompanying drawings.
However, the following description is essentially only illustration
and does not limit the present disclosure, its application, nor its
use. The following description is one example of an engine and a
control device of the engine.
FIG. 1 is a view illustrating a configuration of the
compression-ignition engine. FIG. 2 is a view illustrating a
configuration of a combustion chamber of the engine. FIG. 3 is a
view illustrating a configuration of the combustion chamber and an
intake system. Note that in FIG. 1, an intake side is the left side
in the drawing, and an exhaust side is the right side in the
drawing. In FIGS. 2 and 3, the intake side is the right side in the
drawings, and the exhaust side is the left side in the drawings.
FIG. 4 is a block diagram illustrating a configuration of the
control device of the engine.
An engine 1 is a four-stroke engine which operates by combustion
chambers 17 repeating an intake stroke, a compression stroke, an
expansion stroke, and an exhaust stroke. The engine 1 is mounted on
an automobile with four wheels. The automobile travels by operating
the engine 1. Fuel of the engine 1 is gasoline in this example. The
fuel may be a liquid fuel containing at least gasoline. The fuel
may be gasoline containing, for example, bioethanol.
(Engine Configuration)
The engine 1 includes a cylinder block 12 and a cylinder head 13
placed thereon. A plurality of cylinders 11 are formed inside the
cylinder block 12. In FIGS. 1 and 2, only one cylinder 11 is
illustrated. The engine 1 is a multi-cylinder engine.
A piston 3 is slidably inserted in each cylinder 11. The pistons 3
are connected with a crankshaft 15 through respective connecting
rods 14. Each piston 3 defines the combustion chamber 17, together
with the cylinder 11 and the cylinder head 13. Note that the term
"combustion chamber" may be used in a broad sense. That is, the
term "combustion chamber" may refer to a space formed by the piston
3, the cylinder 11, and the cylinder head 13, regardless of the
position of the piston 3.
As illustrated in the lower figure of FIG. 2, a lower surface of
the cylinder head 13, i.e., a ceiling surface of the combustion
chamber 17, is comprised of a slope 1311 and a slope 1312. The
slope 1311 is a rising gradient from the intake side toward an
injection axial center X2 of an injector 6 (fuel injection valve)
which will be described later. The slope 1312 is a rising gradient
from the exhaust side toward the injection axial center X2. The
ceiling surface of the combustion chamber 17 is a so-called
"pent-roof" shape.
An upper surface of the piston 3 is bulged toward the ceiling
surface of the combustion chamber 17. A cavity 31 is formed in the
upper surface of the piston 3. The cavity 31 is a dent in the upper
surface of the piston 3. The cavity 31 has a shallow pan shape in
this example. The center of the cavity 31 is offset at the exhaust
side with respect to a center axis X1 of the cylinder 11.
A geometric compression ratio of the engine 1 is set 10:1 or higher
and 30:1 or lower. The engine 1 which will be described later
performs SPCCI (SPark Controlled Compression Ignition) combustion
that is a combination of SI (spark ignition) combustion and CI
(compression ignition) combustion in a part of operating ranges.
SPCCI combustion controls the CI combustion using a heat generation
and a pressure buildup by the SI combustion. The engine 1 is the
compression-ignition engine. However, in this engine 1, a
temperature of the combustion chamber 17, when the piston 3 is at a
compression top dead center (i.e., compression end temperature),
does not need to be increased. In the engine 1, the geometric
compression ratio can be set comparatively low. The low geometric
compression ratio becomes advantageous in reduction of cooling loss
and mechanical loss. For engines using regular gasoline (low octane
fuel of which an octane number is about 91), the geometric
compression ratio of the engine 1 is 14:1-17:1, and for those using
high octane gasoline (high octane fuel of which the octane number
is about 96), the geometric compression ratio is 15:1-18:1.
An intake port 18 is formed in the cylinder head 13 for each
cylinder 11. As illustrated in FIG. 3, each intake port 18 has a
first intake port 181 and a second intake port 182. The intake port
18 communicates with the corresponding combustion chamber 17.
Although detailed illustration of the intake port 18 is omitted, it
is a so-called "tumble port." That is, the intake port 18 has such
a shape that a tumble flow is formed in the combustion chamber
17.
Each intake valve 21 is disposed in the intake ports 181 and 182.
The intake valve 21 opens and closes a channel between the
combustion chamber 17 and the intake port 181 or 182. The intake
valves 21 are opened and closed at given timings by a valve
operating mechanism. The valve operating mechanism may be a
variable valve operating mechanism which varies the valve timing
and/or valve lift. In this example, as illustrated in FIG. 4, the
variable valve operating mechanism has an intake-side electric S-VT
(Sequential-Valve Timing) 23. The intake-side electric S-VT 23
continuously varies a rotation phase of an intake cam shaft within
a given angle range. The valve open timing and the valve close
timing of the intake valve 21 vary continuously. Note that the
electric S-VT may be replaced with a hydraulic S-VT, as the intake
valve operating mechanism.
An exhaust port 19 is also formed in the cylinder head 13 for each
cylinder 11. As illustrated in FIG. 3, each exhaust port 19 also
has a first exhaust port 191 and a second exhaust port 192. The
exhaust port 19 communicates with the corresponding combustion
chamber 17.
Each exhaust valve 22 is disposed in the exhaust ports 191 and 192.
The exhaust valve 22 opens and closes a channel between the
combustion chamber 17 and the exhaust port 191 or 192. The exhaust
valves 22 are opened and closed at a given timing by a valve
operating mechanism. The valve operating mechanism may be a
variable valve operating mechanism which varies the valve timing
and/or valve lift. In this example, as illustrated in FIG. 4, the
variable valve operating mechanism has an exhaust-side electric
S-VT 24. The exhaust-side electric S-VT 24 continuously varies a
rotation phase of an exhaust cam shaft within a given angle range.
The valve open timing and the valve close timing of the exhaust
valve 22 change continuously. Note that the electric S-VT may be
replaced with a hydraulic S-VT, as the exhaust valve operating
mechanism.
The intake-side electric S-VT 23 and the exhaust-side electric S-VT
24 adjust length of an overlap period where both the intake valve
21 and the exhaust valve 22 open. If the length of the overlap
period is made longer, the residual gas in the combustion chamber
17 can be purged. Moreover, by adjusting the length of the overlap
period, internal EGR (Exhaust Gas Recirculation) gas can be
introduced into the combustion chamber 17. An internal EGR system
is comprised of the intake-side electric S-VT 23 and the
exhaust-side electric S-VT 24. Note that the internal EGR system
may not be comprised of the S-VT.
The injector 6 is attached to the cylinder head 13 for each
cylinder 11. Each injector 6 directly injects fuel into the
combustion chamber 17. The injector 6 is one example of a fuel
injection part. The injector 6 is disposed in a valley part of the
pent roof where the slope 1311 and the slope 1312 meet. As
illustrated in FIG. 2, the injection axial center X2 of the
injector 6 is located at the exhaust side of the center axis X1 of
the cylinder 11. The injection axial center X2 of the injector 6 is
parallel to the center axis X1. The injection axial center X2 of
the injector 6 and the center of the cavity 31 are in agreement
with each other. The injector 6 faces the cavity 31. Note that the
injection axial center X2 of the injector 6 may be in agreement
with the center axis X1 of the cylinder 11. In such a
configuration, the injection axial center X2 of the injector 6 and
the center of the cavity 31 may be in agreement with each
other.
Although detailed illustration is omitted, the injector 6 is
comprised of a multi nozzle-port type fuel injection valve having a
plurality of nozzle ports. As illustrated by two-dot chain lines in
FIG. 2, the injector 6 injects fuel so that the fuel spreads
radially from the center of the combustion chamber 17. The injector
6 has ten nozzle ports in this example, and the nozzle port is
disposed so as to be equally spaced in the circumferential
direction.
The injectors 6 are connected to a fuel supply system 61. The fuel
supply system 61 includes a fuel tank 63 configured to store fuel,
and a fuel supply passage 62 which connects the fuel tank 63 to the
injector 6. In the fuel supply passage 62, a fuel pump 65 and a
common rail 64 are provided. The fuel pump 65 pumps fuel to the
common rail 64. The fuel pump 65 is a plunger pump driven by the
crankshaft 15 in this example. The common rail 64 stores fuel
pumped from the fuel pump 65 at a high fuel pressure. When the
injector 6 is opened, the fuel stored in the common rail 64 is
injected into the combustion chamber 17 from the nozzle ports of
the injector 6. The fuel supply system 61 can supply fuel to the
injectors 6 at a high pressure of 30 MPa or higher. The pressure of
fuel supplied to the injector 6 may be changed according to the
operating state of the engine 1. Note that the configuration of the
fuel supply system 61 is not limited to the configuration described
above.
An ignition plug 25 is attached to the cylinder head 13 for each
cylinder 11. The ignition plug 25 forcibly ignites a mixture gas
inside the combustion chamber 17. The ignition plug 25 is disposed
at the intake side of the center axis X1 of the cylinder 11 in this
example. The ignition plug 25 is located between the two intake
ports 181 and 182 of each cylinder. The ignition plug 25 is
attached to the cylinder head 13 so as to incline downwardly toward
the center of the combustion chamber 17. As illustrated in FIG. 2,
the electrode of the ignition plug 25 faces to the inside of the
combustion chamber 17 and is located near the ceiling surface of
the combustion chamber 17. Note that the ignition plug 25 may be
disposed at the exhaust side of the center axis X1 of the cylinder
11. Moreover, the ignition plug 25 may be disposed on the center
axis X1 of the cylinder 11.
An intake passage 40 is connected to one side surface of the engine
1. The intake passage 40 communicates with the intake port 18 of
each cylinder 11. Gas introduced into the combustion chamber 17
flows through the intake passage 40. An air cleaner 41 is disposed
in an upstream end part of the intake passage 40. The air cleaner
41 filters fresh air. A surge tank 42 is disposed near the
downstream end of the intake passage 40. A portion of the intake
passage 40 downstream of the surge tank 42 constitutes independent
passages branched from the intake passage 40 for each cylinder 11.
The downstream end of each independent passage is connected to the
intake port 18 of each cylinder 11.
A throttle valve 43 is disposed between the air cleaner 41 and the
surge tank 42 in the intake passage 40. The throttle valve 43
adjusts an introducing amount of the fresh air into the combustion
chamber 17 by adjusting an opening of the throttle valve. That is,
the throttle valve 43 configures an "air adjusting part" which
adjusts the air amount to be supplied into each combustion chamber
17 by increasing and decreasing the amount.
A supercharger 44 is also disposed in the intake passage 40,
downstream of the throttle valve 43. The supercharger 44 boosts gas
to be introduced into the combustion chamber 17. In this example,
the supercharger 44 is a mechanical supercharger driven by the
engine 1. The mechanical supercharger 44 may be a Roots, Lysholm,
Vane, or a centrifugal type.
An electromagnetic clutch 45 is provided between the supercharger
44 and the engine 1. The electromagnetic clutch 45 transmits a
driving force from the engine 1 to the supercharger 44 or
disengages the transmission of the driving force between the
supercharger 44 and the engine 1. As will be described later, an
ECU 10 switches the disengagement and engagement of the
electromagnetic clutch 45 to switch the supercharger 44 between ON
and OFF.
An intercooler 46 is disposed downstream of the supercharger 44 in
the intake passage 40. The intercooler 46 cools gas compressed by
the supercharger 44. The intercooler 46 may be of a water cooling
type or an oil cooling type, for example.
A bypass passage 47 is connected to the intake passage 40. The
bypass passage 47 connects an upstream part of the supercharger 44
to a downstream part of the intercooler 46 in the intake passage 40
so as to bypass the supercharger 44 and the intercooler 46. An air
bypass valve 48 is disposed in the bypass passage 47. The air
bypass valve 48 adjusts a flow rate of gas flowing in the bypass
passage 47.
The ECU 10 fully opens the air bypass valve 48 when the
supercharger 44 is turned OFF (i.e., when the electromagnetic
clutch 45 is disengaged). The gas flowing through the intake
passage 40 bypasses the supercharger 44 and is introduced into the
combustion chamber 17 of the engine 1. The engine 1 operates in a
non-supercharged state, i.e., a natural aspiration state.
When the supercharger 44 is turned ON, the engine 1 operates in a
supercharged state. The ECU 10 adjusts an opening of the air bypass
valve 48 when the supercharger 44 is turned ON (i.e., when the
electromagnetic clutch 45 is engaged). A portion of the gas which
passed through the supercharger 44 flows back upstream of the
supercharger 44 through the bypass passage 47. When the ECU 10
adjusts the opening of the air bypass valve 48, a supercharging
pressure of gas introduced into the combustion chamber 17 changes.
Note that the term "supercharging" as used herein refers to a
situation where the pressure inside the surge tank 42 exceeds an
atmospheric pressure, and "non-supercharging" refers to a situation
where the pressure inside the surge tank 42 becomes below the
atmospheric pressure.
In this example, a supercharging system 49 is comprised of the
supercharger 44, the bypass passage 47, and the air bypass valve
48.
The engine 1 has a swirl generating part which generates a swirl
flow inside the combustion chamber 17. As illustrated in FIG. 3,
the swirl generating part has a swirl control valve 56 attached to
the intake passage 40. Among a primary passage 401 coupled to the
first intake port 181 and a secondary passage 402 coupled to the
second intake port 182, the swirl control valve 56 is disposed in
the secondary passage 402. The swirl control valve 56 is an opening
control valve which is capable of choking a cross section of the
secondary passage 402. When the opening of the swirl control valve
56 is small, since an intake flow rate of air flowing into the
combustion chamber 17 from the first intake port 181 is relatively
large, and an intake flow rate of air flowing into the combustion
chamber 17 from the second intake port 182 is relatively small, the
swirl flow inside the combustion chamber 17 becomes stronger. On
the other hand, when the opening of the swirl control valve 56 is
large, since the intake flow rates of air flowing into the
combustion chamber 17 from the first intake port 181 and the second
intake port 182 become substantially equal, the swirl flow inside
the combustion chamber 17 becomes weaker. When the swirl control
valve 56 is fully opened, the swirl flow will not occur. Note that
the swirl flow circulates counterclockwise in FIG. 3, as
illustrated by white arrows (also see white arrows in FIG. 2).
An exhaust passage 50 is connected to the other side surface of the
engine 1. The exhaust passage 50 communicates with the exhaust port
19 of each cylinder 11. The exhaust passage 50 is a passage through
which exhaust gas discharged from the combustion chambers 17 flows.
Although detailed illustration is omitted, an upstream portion of
the exhaust passage 50 constitutes independent passages branched
from the exhaust passage 50 for each cylinder 11. The upper end of
the independent passage is connected to the exhaust port 19 of each
cylinder 11.
An exhaust gas purification system having a plurality of catalytic
converters is disposed in the exhaust passage 50. Although
illustration is omitted, an upstream catalytic converter is
disposed inside an engine bay. The upstream catalytic converter has
a three-way catalyst 511 and a GPF (Gasoline Particulate Filter)
512. The downstream catalytic converter is disposed outside the
engine bay. The downstream catalytic converter has a three-way
catalyst 513. Note that the exhaust gas purification system is not
limited to the illustrated configuration. For example, the GPF may
be omitted. Moreover, the catalytic converter is not limited to
those having the three-way catalyst. Further, the order of the
three-way catalyst and the GPF may suitably be changed.
Between the intake passage 40 and the exhaust passage 50, an EGR
passage 52 which constitutes an external EGR system is connected.
The EGR passage 52 is a passage for recirculating a portion of the
exhaust gas to the intake passage 40. The upstream end of the EGR
passage 52 is connected between the upstream catalytic converter
and the downstream catalytic converter in the exhaust passage 50.
The downstream end of the EGR passage 52 is connected to an
upstream part of the supercharger 44 in the intake passage 40. EGR
gas flowing through the EGR passage 52 flows into the upstream part
of the supercharger 44 in the intake passage 40, without passing
through the air bypass valve 48 of the bypass passage 47.
An EGR cooler 53 of water cooling type is disposed in the EGR
passage 52. The EGR cooler 53 cools the exhaust gas. An EGR valve
54 is also disposed in the EGR passage 52. The EGR valve 54 adjusts
a flow rate of the exhaust gas flowing through the EGR passage 52.
By adjusting the opening of the EGR valve 54, an amount of the
cooled exhaust gas, i.e., a recirculating amount of external EGR
gas can be adjusted.
In this example, an EGR system 55 is comprised of the external EGR
system and the internal EGR system. The external EGR system can
supply the lower-temperature exhaust gas to the combustion chamber
17 than the internal EGR system.
In FIGS. 1 and 4, an alternator 57 is connected with the crankshaft
15. The alternator 57 is driven by the engine 1. An ECU 10
(described later) can adjust the torque outputted from the engine 1
by increasing the load of the alternator 57.
The control device for the compression ignition engine includes the
ECU (Engine Control Unit) 10 for operating the engine 1. The ECU 10
is a controller based on a known microcomputer, and as illustrated
in FIG. 4, includes a processor such as a central processing unit
(CPU) 101 which executes programs, a memory 102 which is comprised
of, for example, RAM (Random Access Memory) and/or ROM (Read Only
Memory) and stores the programs and data, and an input/output bus
103 through which an electrical signal is inputted and outputted.
The ECU 10 is one example of the "control device."
As illustrated in FIGS. 1 and 4, various kinds of sensors SW1-SW17
are connected to the ECU 10. The sensors SW1-SW17 output signals to
the ECU 10. The sensors include the following sensors:
Airflow sensor SW1: Disposed downstream of the air cleaner 41 in
the intake passage 40, and measures a flow rate of fresh air
flowing through the intake passage 40;
First intake-air temperature sensor SW2: Disposed downstream of the
air cleaner 41 in the intake passage 40, and measures the
temperature of fresh air flowing through the intake passage 40;
First pressure sensor SW3: Disposed downstream of the connected
position of the EGR passage 52 in the intake passage 40 and
upstream of the supercharger 44, and measures the pressure of gas
flowing into the supercharger 44;
Second intake-air temperature sensor SW4: Disposed downstream of
the supercharger 44 in the intake passage 40 and upstream of the
connected position of the bypass passage 47, and measures the
temperature of gas flowed out of the supercharger 44;
Second pressure sensor SW5: Attached to the surge tank 42, and
measures the pressure of gas downstream of the supercharger 44;
Pressure sensors SW6: Attached to the cylinder head 13
corresponding to each cylinder 11, and measures the pressure inside
each combustion chamber 17;
Exhaust temperature sensor SW7: Disposed in the exhaust passage 50,
and measures the temperature of the exhaust gas discharged from the
combustion chamber 17;
Linear O.sub.2 sensor SW8: Disposed upstream of the upstream
catalytic converter in the exhaust passage 50, and measures the
oxygen concentration of the exhaust gas;
Lambda O.sub.2 sensor SW9: Disposed downstream of the three-way
catalyst 511 in the upstream catalytic converter, and measures the
oxygen concentration of the exhaust gas;
Water temperature sensor SW10: Attached to the engine 1 and
measures the temperature of coolant;
Crank angle sensor SW11: Attached to the engine 1 and measures the
rotation angle of the crankshaft 15;
Accelerator opening sensor SW12: Attached to an accelerator pedal
mechanism and measures the accelerator opening corresponding to an
operating amount of the accelerator pedal;
Intake cam angle sensor SW13: Attached to the engine 1 and measures
the rotation angle of an intake cam shaft;
Exhaust cam angle sensor SW14: Attached to the engine 1 and
measures the rotation angle of an exhaust cam shaft;
EGR pressure difference sensor SW15: Disposed in the EGR passage 52
and measures a pressure difference between the upstream and the
downstream of the EGR valve 54;
Fuel pressure sensor SW16: Attached to the common rail 64 of the
fuel supply system 61, and measures the pressure of fuel supplied
to the injector 6; and
Third intake-air temperature sensor SW17: Attached to the surge
tank 42, and measures the temperature of gas inside the surge tank
42, i.e., the temperature of intake air introduced into the
combustion chamber 17.
Each of the sensors SW1-SW17 is one example of a measuring part
which measures a parameter related to the operating of the engine
1.
The ECU 10 determines the operating state of the engine 1 based on
the signals of the sensors SW1-SW17, and calculates a control
amount of each device according to the control logic defined
beforehand. The control logic is stored in the memory 102. The
control logic includes calculating a target amount and/or the
control amount by using a map stored in the memory 102.
The ECU 10 outputs electrical signals according to the calculated
control amounts to the injectors 6, the ignition plugs 25, the
intake-side electric S-VT 23, the exhaust-side electric S-VT 24,
the fuel supply system 61, the throttle valve 43, the EGR valve 54,
the electromagnetic clutch 45 of the supercharger 44, the air
bypass valve 48, the swirl control valve 56, and the alternator
57.
For example, the ECU 10 sets a target torque of the engine 1 based
on the signal of the accelerator opening sensor SW12 and the map,
and determines a target supercharging pressure. The ECU 10 then
performs a feedback control for adjusting the opening of the air
bypass valve 48 based on the target supercharging pressure and the
pressure difference before and after the supercharger 44 obtained
from the signals of the first pressure sensor SW3 and the second
pressure sensor SW5 so that the supercharging pressure becomes the
target supercharging pressure.
Moreover, the ECU 10 sets a target EGR rate (i.e., the rate of EGR
gas to entire gas inside the combustion chamber 17) based on the
operating state of the engine 1 and the map. The ECU 10 then
determines a target EGR gas amount based on the target EGR rate and
an inhaled air amount based on the signal of the accelerator
opening sensor SW12, and performs feedback control for adjusting
the opening of the EGR valve 54 based on the pressure difference
before and after the EGR valve 54 obtained from the signal of the
EGR pressure difference sensor SW15 so that the external EGR gas
amount introduced into the combustion chamber 17 becomes the target
EGR gas amount.
Further, the ECU 10 performs an air-fuel ratio feedback control
when a given control condition is satisfied. For example, the ECU
10 adjusts the fuel injection amount of the injector 6 based on the
oxygen concentration of the exhaust gas which is measured by the
linear O2 sensor SW8 and the lambda O2 sensor SW9 so that the
air-fuel ratio of the mixture gas becomes a desired value.
Note that the details of other controls of the engine 1 executed by
the ECU 10 will be described later.
(Concept of SPCCI Combustion)
The engine 1 performs combustion by compressed self-ignition under
a given operating state, mainly to improve fuel consumption and
emission performance. The combustion by self-ignition varies
largely in the timing of the self-ignition, if the temperature
inside the combustion chamber 17 before a compression starts is
nonuniform. Thus, the engine 1 performs SPCCI combustion which is a
combination of SI combustion and CI combustion.
SPCCI combustion is combustion in which the ignition plug 25
forcibly ignites the mixture gas inside the combustion chamber 17
so that the mixture gas carries out SI combustion by flame
propagation, and the temperature inside the combustion chamber 17
increases by the heat generation of SI combustion and the pressure
inside the combustion chamber 17 increases by the flame propagation
so that unburnt mixture gas carries out CI combustion by
self-ignition.
By adjusting the heat amount of SI combustion, the variation in the
temperature inside the combustion chamber 17 before a compression
starts can be absorbed. By the ECU 10 adjusting the ignition
timing, the mixture gas can be self-ignited at a target timing.
In SPCCI combustion, the heat release of SI combustion is slower
than the heat release in CI combustion. As illustrated in FIG. 5,
the waveform of the heat release rate of SI combustion in SPCCI
combustion is smaller in the rising slope than the waveform in CI
combustion. In addition, SI combustion is slower in the pressure
fluctuation (dp/d.theta.) inside the combustion chamber 17 than CI
combustion.
When the unburnt mixture gas self-ignites after SI combustion is
started, the waveform slope of the heat release rate may become
steeper. The waveform of the heat release rate may have an
inflection point X at a timing of starting CI combustion
(.theta.ci).
After the start in CI combustion, SI combustion and CI combustion
are performed in parallel. Since CI combustion has a larger heat
release than SI combustion, the heat release rate becomes
relatively large. However, since CI combustion is performed after a
compression top dead center, the waveform slope of the heat release
rate does not become too steep. The pressure fluctuation in CI
combustion (dp/d.theta.) also becomes comparatively slow.
The pressure fluctuation (dp/d.theta.) can be used as an index
representing combustion noise. As described above, since SPCCI
combustion can reduce the pressure fluctuation (dp/d.theta.), it is
possible to avoid excessive combustion noise. Combustion noise of
the engine 1 can be kept below a tolerable level.
SPCCI combustion is completed when CI combustion is finished. CI
combustion is shorter in the combustion period than SI combustion.
The end timing of SPCCI combustion becomes earlier than SI
combustion.
The heat release rate waveform of SPCCI combustion is formed so
that a first heat release rate waveform Q.sub.SI formed by SI
combustion and a second heat release rate waveform Q.sub.CI formed
by CI combustion continue in this order.
Here, a SI ratio is defined as a parameter indicative of a
characteristic of SPCCI combustion. The SI ratio is defined as an
index related to a ratio of an amount of heat generated by SI
combustion to the entire amount of heat generated by SPCCI
combustion. The SI ratio is a ratio of amount of heat generated by
the two combustions of different combustion forms. When the SI
ratio is high, the ratio of SI combustion is high, and on the other
hand, when the SI ratio is low, the ratio of CI combustion is high.
The SI ratio may be defined as a ratio of the amount of heat
generated by SI combustion to the amount of heat generated by CI
combustion. That is, if the crank angle at which CI combustion
starts in SPCCI combustion is a CI combustion start timing
.theta.ci, the SI ratio may be equal to Q.sub.SI/Q.sub.CI (SI
ratio=Q.sub.SI/Q.sub.CI) based on an area Q.sub.SI of SI combustion
on advance side of .theta.ci and an area Q.sub.CI of CI combustion
on retard side including .theta.ci, in the waveform 801 illustrated
in FIG. 5.
The engine 1 may generate a strong swirl flow inside the combustion
chamber 17, when performing SPCCI combustion. In more detail, the
engine 1 generates the strong swirl flow inside the combustion
chamber 17 when SPCCI combustion of mixture gas leaner than the
stoichiometric air-fuel ratio is carried out. The "strong swirl
flow" may be defined as a flow having a swirl ratio of, for
example, 4:1 or higher. The swirl ratio can be defined as a value
obtained by subtracting an integrated value of measurements of an
intake air flow transverse angular velocity for every valve lift by
an engine angular velocity. Although illustration is omitted, the
intake air flow transverse angular velocity can be obtained based
on measurements by using known rig test equipment.
When the strong swirl flow is generated inside the combustion
chamber 17, the swirl flow is stronger in the outer circumferential
part of the combustion chamber 17, while the swirl flow is
relatively weaker in the central part. By the injector 6 injecting
fuel into the combustion chamber 17 where the strong swirl flow is
formed, the mixture gas can be stratified in which the mixture gas
in the central part of the combustion chamber 17 is relatively
dense, while the mixture gas in the outer circumferential part is
relatively lean.
(Engine Operating Range)
FIGS. 6 and 7 illustrate maps according to the control of the
engine 1. The maps are stored in the memory 102 of the ECU 10. The
maps includes three kinds of maps: a map 501, a map 502, and a map
503. The ECU 10 uses one selected from the three kinds of maps 501,
502, and 503 for the control of the engine 1 according to a wall
temperature of the combustion chamber 17 (or an engine water
temperature), a temperature of intake air, and the atmospheric
pressure. Note that the details of the selection of the three kinds
of maps 501, 502, and 503 will be described later.
The first map 501 is a map when the engine 1 is warm. The second
map 502 is a map when the engine 1 is half-warm. The third map 503
is a map when the engine 1 is cold.
The maps 501, 502, and 503 are defined by the load and the engine
speed of the engine 1. The first map 501 is divided roughly into
three areas according to the load and the engine speed. Concretely,
the three areas are [1] a low load area A1 which includes idle
operation and extends over a low speed range to a middle speed
range, [2] middle-to-high load areas A2, A3, and A4 where the load
is higher than the low load area A1, [3] a high speed area A5 where
the engine speed is higher than the low load area A1, and the
middle-to-high load areas A2, A3, and A4. The middle-to-high load
areas A2, A3, and A4 are further divided into a middle load area
A2, a high-load middle-speed area A3 where the load is higher than
the middle load area A2, and a high-load low-speed area A4 where
the engine speed is lower than the high-load middle-speed area
A3.
The second map 502 is divided roughly into two areas. Concretely,
the two areas are [1] low-and-middle speed areas B1, B2, and B3,
and [2] a high speed area B4 where the engine speed is higher than
the low-and-middle speed areas B1, B2, and B3. The low-and-middle
speed area B1, B2, and B3 are further divided into a low-and-middle
load area B1 equivalent to the low load area A1 and the middle load
area A2, a high-load middle-speed area B2, and a high-load
low-speed area B3.
The third map 503 is not divided into a plurality of areas, but has
only one area C1.
Here, the low speed area, the middle speed area, and the high speed
area may be defined by substantially equally dividing the entire
operating range of the engine 1 into three areas in the engine
speed direction. In the example of FIG. 6, the engine speed is
defined to be a low speed if the engine speed is lower than the
engine speed N1, a high speed if the engine speed is higher than or
equal to the engine speed N2, and a middle speed if the engine
speed is higher than or equal to the engine speed N1 and lower than
the engine speed N2. For example, the engine speed N1 may be about
1,200 rpm, and the engine speed N2 may be about 4,000 rpm.
Moreover, the low load area may be an area including an operating
state with the light load, the high load area may be an area
including an operating state with full load, and the middle load
area may be an area between the low load area and the high load
area. Moreover, the low load area, the middle load area, and the
high load area may be defined by substantially equally dividing the
entire operating range of the engine 1 into three areas in the load
direction.
The maps 501, 502, and 503 of FIG. 6 illustrate states of the
mixture gas and combustion modes in the respective ranges. The map
504 of FIG. 7 corresponds to the first map 501, and illustrates
states of the mixture gas and combustion modes in the respective
ranges in this map, the opening of the swirl control valve 56 in
the respective ranges, driving/non-driving ranges of the
supercharger 44, and a range where the reduced-cylinder operation
is performed (A/F lean low load range). The engine 1 performs SPCCI
combustion in the low load area A1, the middle load area A2, the
high-load middle-speed area A3, the high-load low-speed area A4,
and the low-and-middle load area B1, the high-load middle-speed
area B2, and the high-load low-speed area B3. The engine 1 performs
SI combustion in other ranges, such as the high speed area A5, the
high speed area B4, and the area C1.
(Operation of Engine in Each Area)
Below, the operation of the engine 1 in each area of the map 504 of
FIG. 7 is described in detail.
(Low Load Area)
The engine 1 performs SPCCI combustion when the engine 1 operates
in the low load area A1.
In order to improve the fuel efficiency of the engine 1, the EGR
system 55 introduces the EGR gas into the combustion chamber 17.
For example, the intake-side electric S-VT 23 and the exhaust-side
electric S-VT 24 are provided with a positive overlap period where
both the intake valve 21 and the exhaust valve 22 are opened near
an exhaust top dead center. Part of the exhaust gas discharged from
the combustion chamber 17 into the intake port 18 and the exhaust
port 19 is re-introduced into the combustion chamber 17. Since the
hot exhaust gas is introduced into the combustion chamber 17, the
temperature inside the combustion chamber 17 increases. Thus, it
becomes advantageous to stabilize SPCCI combustion. Note that the
intake-side electric S-VT 23 and the exhaust-side electric S-VT 24
may be provided with a negative overlap period where both the
intake valve 21 and the exhaust valve 22 are closed.
Moreover, the swirl generating part forms the strong swirl flow
inside the combustion chamber 17. The swirl ratio is four or
higher, for example. The swirl control valve 56 is fully closed or
at a given opening (closed to some extent). As described above,
since the intake port 18 is the tumble port, an inclined swirl flow
having a tumble component and a swirl component is formed in the
combustion chamber 17.
The injector 6 injects fuel into the combustion chamber 17 a
plurality of times during the intake stroke. The mixture gas is
stratified by the multiple fuel injections and the swirl flow
inside the combustion chamber 17.
The fuel concentration of the mixture gas in the central part of
the combustion chamber 17 is denser or richer than the fuel
concentration in the outer circumferential part. For example, the
air-fuel ratio (A/F) of the mixture gas in the central part is 20:1
or higher and 30:1 or lower, and the A/F of the mixture gas in the
outer circumferential part is 35 or higher. Note that the value of
the A/F is a value when the mixture gas is ignited, and the same
applies to the following description. Since the A/F of the mixture
gas near the ignition plug 25 is set 20:1 or higher and 30:1 or
lower, generation of raw NO.sub.x during SI combustion can be
reduced. Moreover, since the A/F of the mixture gas in the outer
circumferential part is set to 35 or higher, CI combustion
stabilizes.
The A/F of the mixture gas is leaner than a stoichiometric air-fuel
ratio throughout the combustion chamber 17 (i.e., the excess air
ratio .lamda.>1: "lean air-fuel ratio"). In more detail, the A/F
of the mixture gas is 25:1 or higher and 31:1 or lower throughout
the combustion chamber 17. Thus, the generation of raw NO.sub.x can
be reduced and the exhaust emission performance can be
improved.
After the fuel injection is finished, the ignition plug 25 ignites
the mixture gas in the central part of the combustion chamber 17 at
a given timing before a compression top dead center. The ignition
timing may be during a final stage of the compression stroke. The
compression stroke may be equally divided into three, an initial
stage, a middle stage, and a final stage, and this final stage may
be used as the final stage of the compression stroke described
above.
As described above, since the mixture gas in the central part has
the relatively high fuel concentration, the ignitability improves
and SI combustion by flame propagation stabilizes. By SI combustion
being stabilized, CI combustion begins at a suitable timing. Thus,
the controllability in CI combustion improves in SPCCI combustion.
Further, the generation of the combustion noise is reduced.
Moreover, since the A/F of the mixture gas is made leaner than the
stoichiometric air fuel ratio to perform SPCCI combustion, the fuel
efficiency of the engine 1 can be significantly improved. Note that
the low load area A1 corresponds to the Layer 3 described later.
The layer 3 extends to the low load operating area and includes the
minimum load operating state.
(Reduced-Cylinder Operation)
As illustrated in FIG. 7, in the low-load range A1 (the range of
"Layer 3"), the reduced-cylinder operation is performed in the
low-load range (A/F lean low-load range) where the load is the
smallest. In other low-load ranges where the load is larger, the
all-cylinder operation is normally performed. In the A/F lean
low-load range, for example, if indicated as a Brake Mean Effective
Pressure (BMEP), the pressure may be within a range below 200 kPa.
Note that, BMEP does not express the load itself, but a value
obtained by multiplying BMEP by the displacement is proportional to
an axial torque.
Thus, in the operating range where BMEP is, for example, below 200
kPa, a throttle loss (pumping loss) of the engine 1 during
combustion becomes relatively large. Therefore, in such an A/F lean
low-load range, the reduced-cylinder operation (cylinder pause
operation) in which SPCCI combustion is not performed in some of
the plurality of combustion chambers 17 (in this embodiment, the
combustion chambers 17 of two cylinders among the four cylinders)
is performed.
In the all-cylinder operation, SPCCI combustion is performed in all
the combustion chambers 17. On the other hand, in the
reduced-cylinder operation, although SPCCI combustion is performed
in some of the plurality of combustion chambers 17, SPCCI
combustion is not performed by suspending the fuel injection (a
so-called "fuel cutoff") in other combustion chambers 17.
In the reduced-cylinder operation, the intake valves 21 and the
exhaust valves 22 are driven to perform the intake and exhaust
processings in the combustion chambers 17 where SPCCI combustion is
not performed, similar to the combustion chambers 17 where SPCCI
combustion is performed. By performing such a reduced-cylinder
operation, since the fuel amount relatively increases in the
combustion chambers 17 where SPCCI combustion is performed, the
throttle loss is reduced and the stable SPCCI combustion can be
realized, even when the entire amount of fuel supplied according to
the target torque is very little.
Note that the change processing between the reduced-cylinder
operation and the all-cylinder operation will be described
later.
(Middle-to-High Load Area)
When the engine 1 operates in the middle-to-high load area (A2, A3,
and A4), the engine 1 also performs SPCCI combustion, similar to
the low load area A1.
The EGR system 55 introduces the EGR gas into the combustion
chamber 17. For example, the intake-side electric S-VT 23 and the
exhaust-side electric S-VT 24 are provided with a positive overlap
period where both the intake valve 21 and the exhaust valve 22 are
opened near an exhaust top dead center. Internal EGR gas is
introduced into the combustion chamber 17. Moreover, the EGR system
55 introduces the exhaust gas cooled by the EGR cooler 53 into the
combustion chamber 17 through the EGR passage 52. That is, the
external EGR gas with a lower temperature than the internal EGR gas
is introduced into the combustion chamber 17. The external EGR gas
adjusts the temperature inside the combustion chamber 17 to a
suitable temperature. The EGR system 55 reduces the amount of the
EGR gas as the engine load increases. The EGR system 55 may not
recirculate the EGR gas containing the internal EGR gas and the
external EGR gas during the full load.
Moreover, in the middle load area A2 and the high-load middle-speed
area A3, the swirl control valve 56 is fully closed or at a given
opening (closed to some extent). On the other hand, in the
high-load low-speed area A4, the swirl control valve 56 is
open.
The A/F of the mixture gas is a stoichiometric air-fuel ratio
(A/F.apprxeq.14.7:1) throughout the combustion chamber 17, or is
substantially the stoichiometric air-fuel ratio. By the three-way
catalysts 511 and 513 purifying the exhaust gas discharged from the
combustion chamber 17, the exhaust emission performance of the
engine 1 improves. The A/F of the mixture gas may be defined within
purification windows of the three-way catalysts. The excess air
ratio .lamda. of the mixture gas may also be 1.0.+-.0.2. Note that
while the engine 1 operates in the high-load middle-speed range A3
including the full load (i.e., the maximum load), the A/F of the
mixture gas may be the stoichiometric air-fuel ratio or richer than
the stoichiometric air-fuel ratio throughout the combustion chamber
17 (i.e., the excess air ratio .lamda. of the mixture gas is
.lamda..ltoreq.1).
Since the EGR gas is introduced into the combustion chamber 17, a
gas-fuel ratio (G/F) which is a weight ratio of the entire gas to
the fuel in the combustion chamber 17 becomes leaner than the
stoichiometric air fuel ratio. The G/F of the mixture gas may be
18:1 or higher. Thus, a generation of a so-called "knock" is
avoided. The G/F may be set 18:1 or higher and 30:1 or lower.
Alternatively, G/F may be set 18:1 or higher and 50:1 or lower.
When the load of the engine 1 is the middle load, the injector 6
performs a plurality of fuel injections during an intake stroke.
The injector 6 may perform the first injection in the first half of
the intake stroke, and may perform the second injection in the
second half of the intake stroke.
Moreover, when the load of the engine 1 is the high load, the
injector 6 injects fuel in the intake stroke.
The ignition plug 25 ignites the mixture gas at a given timing near
a compression top dead center after the fuel injection. When the
load of the engine 1 is the middle load, the ignition plug 25 may
ignite before the compression top dead center. When the load of the
engine 1 is the high load, the ignition plug 25 may ignite after
the compression top dead center.
By performing SPCCI combustion with A/F of the mixture gas being
the stoichiometric air-fuel ratio, exhaust gas discharged from the
combustion chamber 17 can be purified using the three-way catalysts
511 and 513. Moreover, by introducing EGR gas into the combustion
chamber 17 to dilute the mixture gas, the fuel efficiency of the
engine 1 improves. Note that the middle-to-high load areas A2, A3,
and A4 correspond to Layer 2 described later. Layer 2 extends to
the high load area and includes the maximum load operating
state.
(Operation of Supercharger)
Here, as illustrated in the map 504 of FIG. 7, the supercharger 44
is OFF (refer to S/C OFF, the area with dots), in a part of the low
load area A1 and a part of the middle load area A2. In detail, the
supercharger 44 is OFF in a partial range of the low load area A1
on the low speed side. In a partial range of the low load area A1
on the high speed side, the supercharger 44 is ON in order to
secure an intake air filling amount required corresponding to an
increase in the engine speed. Moreover, the supercharger 44 is OFF
in a partial range of the middle load area A2 on the low-load
low-speed side. The supercharger 44 is ON in a partial range of the
middle load area A2 on the high load side, in order to secure an
intake air filling amount required corresponding to an increase in
the fuel injection amount. Moreover, the supercharger 44 is ON also
in a partial range of the middle load area A2 on the high speed
side.
Note that the supercharger 44 is ON (refer to S/C ON) entirely in
the high-load middle-speed area A3, the high-load low-speed area
A4, and the high speed area A5.
(High-Speed Area)
As the engine speed increases, a time required for changing the
crank angle by 1.degree. becomes shorter. Thus, it becomes
difficult to stratify the mixture gas inside the combustion chamber
17. As the engine speed increases, it becomes difficult to perform
SPCCI combustion.
Thus, while the engine 1 is operating in the high-speed area A5,
the engine 1 performs not SPCCI combustion but SI combustion. Note
that the high-speed area A5 stretches entirely in the load
direction from low load to high load.
The EGR system 55 introduces EGR gas into the combustion chamber
17. The EGR system 55 reduces an amount of EGR gas as the load
increases. The EGR system 55 may make EGR gas zero when the engine
is operating with full load.
The swirl control valve 56 is fully open. A swirl flow does not
occur inside the combustion chamber 17, but only a tumble flow
occurs. By fully opening the swirl control valve 56, it becomes
possible to improve the filling efficiency and reduce a pumping
loss.
Fundamentally, an air-fuel ratio (A/F) of mixture gas is a
stoichiometric air-fuel ratio (A/F.apprxeq.14.7:1) entirely in the
combustion chamber 17. An excess air ratio .lamda. of mixture gas
may be set to 1.0.+-.0.2. Note that while the engine 1 is operating
with near the full load state, the excess air ratio .lamda. of
mixture gas may be less than one.
The injector 6 starts a fuel injection on intake stroke. The
injector 6 injects fuel at once. By starting the fuel injection on
intake stroke, homogeneous or substantially homogeneous mixture gas
is formed inside the combustion chamber 17. Moreover, since a
longer vaporizing time of the fuel can be secured, unburnt fuel
loss can also be reduced.
The ignition plug 25 ignites the mixture gas at a suitable timing
before a compression top dead center after the completion of the
fuel injection.
(Layer Structure of Map)
The maps 501, 502, and 503 of the engine 1 illustrated in FIG. 6
are comprised of a combination of three layers: Layer 1, Layer 2,
and Layer 3, as illustrated in FIG. 8.
Layer 1 is a base layer. Layer 1 extends entirely in the operating
range of the engine 1. Layer 1 corresponds to the entire third map
503.
Layer 2 is a layer superimposed on Layer 1. Layer 2 corresponds to
a part of the operating range of the engine 1. Concretely, Layer 2
corresponds to the low-and-middle speed areas B1, B2, and B3 of the
second map 502.
Layer 3 is a layer superimposed on Layer 2. Layer 3 corresponds to
the low load area A1 of the first map 501.
Layer 1, Layer 2, and Layer 3 are selected according to the wall
temperature of the combustion chamber 17 (or the engine water
temperature), the temperature of intake air, and the atmospheric
pressure.
When the atmospheric pressure is higher than a given
atmospheric-pressure threshold (e.g., 95 kPa), the wall temperature
of the combustion chamber 17 is higher than a given first wall
temperature (e.g., 80.degree. C.), and the intake air temperature
is higher than a given first intake air temperature (e.g.,
50.degree. C.), Layer 1, Layer 2, and Layer 3 are selected, and the
first map 501 is formed by piling up these Layer 1, Layer 2, and
Layer 3. In the low load area A1 in the first map 501, Layer 3
which is located at the top therein is enabled, in the
middle-to-high load area A2, A3, and A4, Layer 2 which is located
at the top therein is enabled, and in the high speed area A5, Layer
1 is enabled.
When the wall temperature of the combustion chamber 17 is below the
given first wall temperature and higher than a given second wall
temperature (e.g., 30.degree. C.), and the intake air temperature
is below the given first intake air temperature and higher than a
given second intake air temperature (e.g., 25.degree. C.), Layer 1
and Layer 2 are selected. The second map 502 is formed by piling up
these Layer 1 and Layer 2. In the low-and-middle speed areas B1,
B2, and B3 in the second map 502, Layer 2 which is located at the
top therein is enabled, and in the high speed area B4, Layer 1 is
enabled.
When the wall temperature of the combustion chamber 17 is below the
given second wall temperature, and the intake air temperature is
below a given second intake air temperature, only Layer 1 is
selected and the third map 503 is formed by Layer 1.
Note that the wall temperature of the combustion chamber 17 may be
substituted by, for example, the temperature of the cooling water
of the engine 1 measured by the water temperature sensor SW10.
Moreover, the wall temperature of the combustion chamber 17 may be
estimated based on the temperature of cooling water, or other
measurement signals. Moreover, the intake air temperature can be
measured by, for example, the third intake air temperature sensor
SW17 which measures the temperature inside the surge tank 42.
Moreover, the intake air temperature introduced into the combustion
chamber 17 may be estimated based on various kinds of measurement
signals.
As described above, SPCCI combustion is performed by generating the
strong swirl flow inside the combustion chamber 17. Since flame
propagates along the wall of the combustion chamber 17 in SI
combustion, the flame propagation of SI combustion is influenced by
the wall temperature. If the wall temperature is low, the flame of
SI combustion is cooled, thereby delaying the timing of the
compression ignition.
Since CI combustion in SPCCI combustion is performed in an area
from the outer circumferential part to the central part of the
combustion chamber 17, it is influenced by the temperature of the
central part of the combustion chamber 17. CI combustion becomes
unstable if the temperature of the central part is low. The
temperature of the central part of the combustion chamber 17
depends on the temperature of the intake air introduced into the
combustion chamber 17. That is, the temperature of the central part
of the combustion chamber 17 increases as the intake air
temperature becomes higher, and decreases as the intake air
temperature becomes lower.
When the wall temperature of the combustion chamber 17 is below the
given second wall temperature, and the intake air temperature is
below the given second intake air temperature, the stable SPCCI
combustion cannot be performed. Therefore, only Layer 1 which
performs SI combustion is selected, and the ECU 10 operates the
engine 1 based on the third map 503. By the engine 1 performing SI
combustion in all the operating ranges, the combustion stability
can be secured.
When the wall temperature of the combustion chamber 17 is higher
than the given second wall temperature and the intake air
temperature is higher than the given second intake air temperature,
SPCCI combustion of the mixture gas at the substantially
stoichiometric air-fuel ratio (i.e., .lamda..apprxeq.1) can be
stably carried out. Therefore, in addition to Layer 1, Layer 2 is
selected, and the ECU 10 operates the engine 1 based on the second
map 502. By the engine 1 performing SPCCI combustion in the part of
the operating range, the fuel efficiency of the engine 1
improves.
When the wall temperature of the combustion chamber 17 is higher
than the given first wall temperature and the intake air
temperature is higher than the given first intake air temperature,
SPCCI combustion of the mixture gas leaner than the stoichiometric
air-fuel ratio can be stably carried out. Therefore, in addition to
Layer 1 and Layer 2, Layer 3 is selected, and the ECU 10 operates
the engine 1 based on the first map 501. By the engine 1 carrying
out SPCCI combustion of the lean mixture gas in the part of the
operating range, the fuel efficiency of the engine 1 further
improves.
However, if the atmospheric pressure is low, the amount of air
filled up in the combustion chamber 17 decreases. Therefore, it
becomes difficult to make the mixture gas to the given lean
air-fuel ratio. Thus, Layer 3 is selected when the atmospheric
pressure is higher than the given atmospheric-pressure
threshold.
(Control of Layer Selection)
Next, one example of a control related to the layer selection of
the map executed by the ECU 10 is described with reference to a
flowchart of FIG. 9. At Step S91 after a start, the ECU 10 first
reads the signals of the sensors SW1-SW17. At the subsequent Step
S92 the ECU 10 determines whether the wall temperature of the
combustion chamber 17 is higher than 30.degree. C., and the intake
air temperature is higher than 25.degree. C. If the determination
at Step S92 is YES, the process shifts to Step S93, and on the
other hand, if NO, the process shifts to Step S95. The ECU 10
selects only Layer 1 at Step S95. The ECU 10 operates the engine 1
based on the third map 503. The process then returns.
At Step S93 the ECU 10 determines whether the wall temperature of
the combustion chamber 17 is higher than 80.degree. C., and the
intake air temperature is higher than 50.degree. C. If the
determination at Step S93 is YES, the process shifts to Step S94,
and on the other hand, if NO, the process shifts to Step S96.
The ECU 10 selects Layer 1 and Layer 2 at Step S96. The ECU 10
operates the engine 1 based on the second map 502. The process then
returns.
At Step S94, the ECU 10 determines whether the atmospheric pressure
is higher than the atmospheric-pressure threshold. If the
determination at Step S94 is YES, the process shifts to Step S97,
and on the other hand, if NO, the process shifts to Step S96. At
Step S96, the ECU 10 selects Layer 1 and Layer 2 as described
above.
At Step S97, the ECU 10 selects Layer 1, Layer 2, and Layer 3. The
ECU 10 operates the engine 1 based on the first map 501. The
process then returns.
(Change Control of Cylinder Count)
As described above, in this engine 1, the reduced-cylinder
operation is performed in the A/F lean low-load range of the
low-load range A1 by stopping the fuel injection into some of the
combustion chambers 17 (fuel cutoff). Therefore, in the low-load
range A1, a processing to change the operating state between the
all-cylinder operation and the reduced-cylinder operation is
performed. Next, a control for changing the number of cylinders is
described with reference to a flowchart of FIG. 10.
The ECU 10 first determines whether the engine 1 is operated in the
low-load range A1. That is, the ECU 10 determines whether Layer 3
is selected in the selection control of the layer described
previously, in other words, whether the engine 1 is operated in the
low-load range A1 of the first map 501 (Step S101). If Layer 3 is
selected, the ECU 10 determines whether the engine load is smaller
than a given load, for example, whether BMEP is lower than 200 kPa
(Step S102).
As a result, if the engine load is smaller than the given load, the
ECU 10 further determines that the operating range of the engine 1
is the A/F lean low-load range (refer to FIG. 7), and it performs
the reduced-cylinder operation (Step S103). On the other hand, if
the engine load is larger than the given load, the ECU 10
determines that the operating range of the engine 1 is not the A/F
lean low-load range, and it performs the all-cylinder operation
(Step S104).
(Problems in Change Between all-Cylinder Operation and
Reduced-Cylinder Operation)
When the change control is performed, the total amount of fuel
supplied to the engine 1 is held at substantially constant so that
a large torque fluctuation (torque shock) does not occur.
In such a case, since the air amount and the fuel amount in the
combustion chambers 17 where combustion is performed differ greatly
between the reduced-cylinder operation and the all-cylinder
operation, there is a problem such that raw NO.sub.x occurs or the
combustion becomes unstable when changing the operation while
maintaining the operating state of SPCCI combustion.
For example, when changing from the all-cylinder operation with
four cylinders to the reduced-cylinder operation with two
cylinders, it is necessary to inject twice the amount of fuel into
each combustion chamber 17 where combustion is performed in the
reduced-cylinder operation in order to keep the fuel amount
supplied to the engine 1 constant. On the other hand, in order to
maintain the lean air-fuel ratio, it is necessary to supply twice
the amount of air.
Since fuel is directly injected into the combustion chamber 17 by
the injector 6, the time delay (time lag) is very small. On the
other hand, since air is introduced into the combustion chamber 17
through the air intake passage 40 after the throttle valve 43 is
actuated, the time lag occurs.
Therefore, if the operation is changed instantly, since twice the
amount of fuel is injected in the state where the air amount has
not been increased, the air-fuel ratio becomes small instantly.
FIG. 11 illustrates a relation between the generated amount of raw
NO.sub.x and A/F during combustion. As illustrated by a solid line
of a mountain shape, raw NO.sub.x tends to be generated within a
range where A/F is approximately 10 to 25, and has a peak at the
median. In the low-load range A1 where the operation is changed,
SPCCI combustion is performed while the air-fuel ratio is held
within a range of substantially the lean air-fuel ratio (a range
illustrated by an arrow "A/F lean"). If the air-fuel ratio is kept
within the range, raw NO.sub.x will hardly be generated. Moreover,
the stable SPCCI combustion can be realized.
However, as illustrated by an arrow Y1, if the air-fuel ratio
becomes richer or lower at once from the state described above, raw
NO.sub.x will occur and increase rapidly.
On the other hand, if the operation is changed after the increase
in air, while maintaining the fuel amount, since the air-fuel ratio
becomes further leaner and higher than the lean air-fuel ratio as
illustrated by an arrow Y2. Therefore, since raw NO.sub.x is not
generated but the air-fuel ratio becomes excessively lean, the
stable SPCCI combustion becomes difficult.
On the contrary, when changing from the reduced-cylinder operation
to the all-cylinder operation, the number of combustion chambers 17
where combustion is performed are doubled. In order to keep the
fuel amount supplied to the engine 1 constant, it is necessary to
reduce the fuel injection amount to half and to also reduce the air
amount to half, in the combustion chambers 17 where combustion is
performed.
Therefore, in this case, if the operation is changed instantly,
since the fuel is halved without the air amount being reduced, the
air-fuel ratio becomes high at once. Therefore, although raw
NO.sub.x is not generated, the stable SPCCI combustion becomes
difficult because the air-fuel ratio became excessively lean.
On the other hand if the operation is changed after the reduction
in air while maintaining the fuel amount, raw NO.sub.x occurs, as
illustrated by the arrow Y1, because the air-fuel ratio becomes
lower.
Therefore, this engine 1 is devised such that, as will be described
later, the ECU 10 is provided with a cylinder count control module
10a, and when the operating state is changed between the
all-cylinder operation and the reduced-cylinder operation, the
operating state is changed smoothly while preventing the
degradation of the emission performance.
(Basic Control of Engine)
FIG. 12 illustrates a flowchart of a basic control of the engine 1
executed by the ECU 10. The ECU 10 operates the engine 1 according
to the control logic stored in the memory 102. Concretely, the ECU
10 determines the operating state of the engine 1 based on the
signals of the sensors SW1-SW17, sets the target torque, and
calculates for adjustments of the properties inside the combustion
chamber 17, the injection amount, the injection timing, and the
ignition timing so that the engine 1 outputs the target torque.
The ECU 10 controls SPCCI combustion using two parameters of a SI
ratio and .theta.ci, when performing SPCCI combustion. Concretely,
the ECU 10 defines a target SI ratio and a target .theta.ci
corresponding to the operating state of the engine 1, and adjusts
the temperature inside the combustion chamber 17 and the ignition
timing so that an actual SI ratio become in agreement with the
target SI ratio, and an actual .theta.ci becomes in agreement with
the target .theta.ci. The ECU 10 sets the target SI ratio low when
the load of the engine 1 is low, and sets the target SI ratio high
when the load of the engine 1 is high. When the load of the engine
1 is low, both the reduction of combustion noise and the
improvement of fuel efficiency are achieved by increasing the ratio
of CI combustion in SPCCI combustion. When the load of the engine 1
is high, it becomes advantageous in reducing the combustion noise
by raising the ratio of SI combustion in SPCCI combustion.
At Step S121 in the flowchart of FIG. 12, the ECU 10 reads the
signals of the sensors SW1-SW17, and at the subsequent Step S122,
the ECU 10 sets a target acceleration based on the accelerator
opening. At Step S123, the ECU 10 sets a target torque required for
realizing the target acceleration setting.
At Step S124, the ECU 10 determines the operating state of the
engine 1, and determines whether the air-fuel ratio of the mixture
gas is the stoichiometric air-fuel ratio or the substantially
stoichiometric air-fuel ratio (i.e., the excess air ratio
.lamda.=1). At Step S124, the ECU 10 determines whether the engine
1 operates in Layer 1 or Layer 2 (.lamda.=1), or operates in Layer
3 (.lamda..noteq.1). If .lamda.=1, the process shifts to Step S125,
and on the other hand, if .lamda..noteq.1, the process shifts to
Step S129.
Steps S125-S128 correspond to steps for setting a target control
value of each device, when the engine 1 operates in Layer 1 or
Layer 2. At Step S125, the ECU 10 sets a target ignition timing of
the ignition plug 25 based on the target torque setting. At the
subsequent Step S126, the ECU 10 sets a target amount of air filled
up in the combustion chamber 17 based on the target torque setting.
At Step S127, the ECU 10 sets a target fuel injection amount based
on the target air amount setting so that the air-fuel ratio of the
mixture gas becomes the stoichiometric air-fuel ratio or the
substantially stoichiometric air-fuel ratio. Then, at Step S128,
the ECU 10 sets a target throttle opening of the throttle valve 43,
a target SCV opening of the swirl control valve 56, a target EGR
valve opening of the EGR valve 54, a target S-VT phase of the
intake electric S-VT23, and a target S-VT phase of the exhaust
electric S-VT24, based on the target air amount setting.
Steps S129-S1212 correspond to steps for setting the target control
value of each device, when the engine 1 operates in Layer 3. At
Step S129, the ECU 10 sets the target ignition timing of the
ignition plug 25 based on the target torque setting. At the
subsequent Step S1210, the ECU 10 sets the target fuel injection
amount based on the target torque setting. At Step S1211, the ECU
10 sets the target amount of air filled up in the combustion
chamber 17 based on the target injection amount setting so that the
air-fuel ratio of the mixture gas becomes the given lean air-fuel
ratio. As described above, the air-fuel ratio of the mixture gas is
within a range of 25:1 to 31:1. Then, at Step S1212, the ECU 10
sets the target throttle opening of the throttle valve 43, the
target SCV opening of the swirl control valve 56, the target EGR
valve opening of the EGR valve 54, the target S-VT phase of the
intake-side electric S-VT23, and the target S-VT phase of the
exhaust-side electric S-VT24, based on the target air amount
setting.
At Step S1213, the ECU 10 adjusts the throttle opening of the
throttle valve 43, the SCV opening of the swirl control valve 56,
and the EGR valve opening of the EGR valve 54, the S-VT phase of
the intake electric S-VT23, and the S-VT phase of the exhaust
electric S-VT24 so that these parameters become target values set
at Step S128 or Step S1212.
At Step S1214, the ECU 10 causes the injector 6 to inject fuel at a
given timing according to the target injection amount setting, and
at the subsequent Step S1215, the ECU 10 causes the ignition plug
25 to ignite at the set target ignition timing.
(Cylinder Count Control Module 10a)
FIG. 13 illustrates a configuration of a functional block of the
ECU 10 related to the change between the all-cylinder operation and
the reduced-cylinder operation. The functional block includes the
cylinder count control module 10a described above, an all-cylinder
operation module 10b, a reduced-cylinder operation module 10c, and
a determination module 10d.
When a change demand is received, the cylinder count control module
10a outputs signals to the injectors 6, the ignition plugs 25, the
throttle valve 43, the alternator 57, etc. based on the signals of
the sensors SW1-SW17, and executes a preparation control to change
the operation between the all-cylinder operation and the
reduced-cylinder operation. The all-cylinder operation module 10b
performs SPCCI combustion in the combustion chambers of all the
four cylinders within an operating range in the low-load range A1
where the load is larger than the given load. In the A/F lean
low-load range of the low-load range A1, the reduced-cylinder
operation module 10c suspends the fuel injection into the
combustion chambers 17 of two cylinders among the four cylinders
and does not perform SPCCI combustion in the two cylinders, but
injects fuel into the combustion chambers 17 of other two cylinders
and performs SPCCI combustion in the two cylinders.
The determination module 10d determines whether the change between
the all-cylinder operation and the reduced-cylinder operation is
necessary. If the change is necessary, the determination module 10d
outputs the determination result to the cylinder count control
module 10a to demand the change. The cylinder count control module
10a which received the change demand from the determination module
10d executes the preparation control according to the change
demand.
(First Preparation Control Pattern: Change from all-Cylinder
Operation to Reduced-Cylinder Operation)
FIG. 14 illustrates one example of the preparation control for the
change from the all-cylinder operation to the reduced-cylinder
operation (a pattern of a first preparation control). The ECU 10
reads the signals of the sensors SW1-SW17 (Step S141). Next, the
ECU 10 determines whether the change from the all-cylinder
operation to the reduced-cylinder operation is necessary (Step
S142).
Concretely, the determination module 10d of the ECU 10 determines
whether the change from the all-cylinder operation to the
reduced-cylinder operation is necessary based on the operating
state of the engine 1. As a result of the determination, if the
change is necessary, the determination module 10d sets a
reduced-cylinder operation change flag to 1. The ECU 10 determines
whether the reduced-cylinder operation change flag is 1. If the
flag is 1, the process shifts to the step of the preparation
control, and on the other hand, if the flag is not 1, the process
returns without shifting to the process of the preparation
control.
When the preparation control process is started concretely, the ECU
10 first maintains the amount of fuel injected into each combustion
chamber 17 during the change (a fuel amount maintain processing).
That is, the fuel is injected into all the combustion chambers 17
at the fuel amount according to the target injection amount set for
the all-cylinder operation during the change (Step S143).
In the meantime, since the total amount of fuel used for the
combustion of the engine 1 is constant, the torque outputted is
held at substantially constant.
The ECU 10 sets a target air amount in the reduced-cylinder
operation (Step S144). Further, the ECU 10 sets a target throttle
valve opening based on the target air amount setting (Step S145).
Then, the ECU 10 adjusts the opening of the throttle valve 43 so as
to become the target throttle valve opening setting (Step
S146).
Specifically, the ECU 10 outputs a signal to the throttle valve 43
to increase the amount of air supplied to each of the combustion
chambers 17 (an air amount increase processing). When changing from
the all-cylinder operation to the reduced-cylinder operation, the
target air amount relatively increases and the opening of the
throttle valve 43 changes from small to large. Here, the air amount
filled up in the combustion chamber 17 does not increase instantly.
Therefore, the time delay (time lag) occurs by the time the air
amount reaches the target air amount.
The ECU 10 reads an amount of air actually filled up in the
combustion chamber 17 (Step S147). Next, the ECU 10 calculates a
rich limit torque based on the read actual air amount (Step
S148).
(Rich Limit Torque, Retard Limit Torque)
Although the engine is operated in the low-load range A1 at the
lean air-fuel ratio where raw NO.sub.x is hardly generated. The
rich limit torque means a torque obtained from the engine 1 when
SPCCI combustion is performed at an air-fuel ratio when the fuel
amount is increased with respect to the actual air amount from the
lean air-fuel ratio to such a limit below which raw NO.sub.x is not
generated (a rich limit A/F corresponding to a threshold which will
be described later).
In other words, the rich limit A/F (threshold) is an air-fuel ratio
lower than the target lean air-fuel ratio of the low-load range A1,
and if air-fuel ratio exceeds the threshold, there is a possibility
that raw NO.sub.x occurs. The rich limit torque corresponds to an
upper limit of the torque which can be generated under the
condition in which the air-fuel ratio is made at such a rich limit
A/F based on the actual air amount. The rich limit torque is an
imaginary torque calculated by the ECU 10.
On the other hand, the retard limit torque (used in a second
preparation control pattern which will be described later) is a
torque of the engine 1 obtained by carrying out SPCCI combustion of
the mixture gas at a lean air-fuel ratio in a state where the
ignition timing is retarded as much as possible. If the ignition
timing is excessively retarded, CI combustion in SPCCI combustion
may not occur, or the stability of SI combustion may be reduced.
The engine 1 which performs SPCCI combustion has a retard limit of
the ignition timing. The retard limit torque corresponds to a lower
limit of the torque of the engine 1 which can be reduced by
retarding the ignition timing under a condition where the air-fuel
ratio is made at the lean air-fuel ratio based on the actual air
amount. The retard limit torque is also an imaginary torque
calculated by the ECU 10.
FIG. 15 is a block diagram illustrating a calculation procedure of
the retard limit torque. The ECU 10 calculates the retard limit
torque based on the thermal efficiency of the engine 1 at the
retard limit. The thermal efficiency of the engine 1 at the retard
limit is calculated based on the thermal efficiency of the engine 1
at MBT (Minimum advance for Best Torque), and the mfb50 position at
the retard limit. The mfb50 position at the retard limit is a crank
angle at which a mass combustion rate (Mass Fraction Burnt: mfb)
becomes 50% in a combustion waveform when the ignition timing is
retarded as much as possible.
The ECU 10 calculates the mfb50 position at the retard limit based
on the engine speed, the filling efficiency, a map 151 determined
beforehand. The map 151 defines a relation between the engine
operating state (the engine speed, and the filling efficiency,
i.e., corresponding to the load of the engine 1), and the mfb50
position at the retard limit. As the engine speed decreases, and
the load increases (i.e., the filling efficiency is high), the fuel
amount increases and the combustion stability becomes higher, and
since a time from an ignition to combustion becomes longer even if
the ignition timing is retarded, a misfire etc. can be reduced. The
ignition timing can be more retarded as the engine speed decreases
and the load increases. The mfb50 position at the retard limit is
retarded as the engine speed decreases and the load increases, and
is advanced as the engine speed increases and the load decreases
(i.e., the filling efficiency is low).
Note that, although the mfb50 position at the retard limit is
determined using the map 151, the mfb50 position at the retard
limit may be calculated using a model in consideration of LNV
(Lowest Normalized Value).
The ECU 10 sets an efficiency of MBT based on the mfb50 position at
the retard limit and the map 152 determined beforehand. The map 152
defines a relation between the mfb50 position at the retard limit
and the efficiency of MBT. The efficiency of MBT becomes "1" if the
mfb50 position at the retard limit is a given crank angle on the
advance side, and approaches zero as the mfb50 position at the
retard limit is retarded.
The map 152 defines a reference curve (refer to a solid line), and
this curve is corrected according to the operating state of the
engine 1. The map 153 relates to an efficiency slope for correcting
the reference curve of the map 152. The map 153 defines a relation
of the engine speed, the filling efficiency, and the efficiency
slope. The efficiency slope decreases as the engine speed decreases
and the load decreases, and increases as the engine speed increases
and the load increases.
The reference curve of the map 152 illustrated by the solid line
falls downward as the efficiency slope defined based on the map 153
increases, as illustrated by a broken line, and it goes up upward
as the efficiency slope decreases. The ECU 10 defines the
efficiency of MBT at the retard limit based on the map 152 which is
corrected by the efficiency slope (refer to one-dot chain line
arrows).
The ECU 10 defines the thermal efficiency at the retard limit based
on the efficiency of MBT and the map 154 determined beforehand. The
map 154 defines a relation of the engine speed, the filling
efficiency, and the thermal efficiency at MBT. The thermal
efficiency at MBT decreases as the engine speed decreases and the
load decreases, and increases as the engine speed increases and the
load increases. The ECU 10 defines the thermal efficiency at MBT in
an operating state of the engine 1 based on the engine speed, the
filling efficiency, and the map 154, and calculates the thermal
efficiency at the retard limit based on the thermal efficiency at
MBT and the efficiency of MBT defined in the map 152.
When the thermal efficiency at the retard limit is calculated, the
ECU 10 then calculates a torque corresponding to the thermal
efficiency concerned (i.e., the retard limit torque) based on the
thermal efficiency at the retard limit, a volume per cylinder, and
a calorific value of an injection amount at which the air-fuel
ratio of the mixture gas becomes the lean air-fuel ratio.
FIG. 16 is a block diagram illustrating a calculation procedure of
the rich limit torque. The ECU 10 calculates the rich limit torque
based on the thermal efficiency of the engine 1 at the rich limit.
The thermal efficiency of the engine 1 at the rich limit is
calculated based on the thermal efficiency of the engine 1 at MBT
and the mfb50 position at the rich limit. The mfb50 position at the
rich limit indicates a crank angle at which the mass combustion
rate becomes 50% in a waveform when the mixture gas of the air-fuel
ratio at which the generation of raw NO.sub.x is reduced
combusts.
The ECU 10 calculates the mfb50 position at the rich limit based on
the engine speed, a rich limit injection amount, and the map 161
determined beforehand. The map 161 defines a relation of the engine
speed, the rich limit injection amount, and the mfb50 position. The
rich limit injection amount is an upper limit of the injection
amount below which the generation of raw NO.sub.x is reduced. The
mfb50 position at the rich limit is retarded as the engine speed
decreases and the load decreases, and is advanced as the engine
speed increases and the load increases.
The map 162, the map 163, and the map 164 in FIG. 16 are the same
as the map 152, the map 153, and the map 154 in FIG. 15,
respectively.
The ECU 10 sets the efficiency of MBT based on the mfb50 position
at the rich limit and the map 162 determined beforehand (refer to
the one-dot chain line arrows).
The reference curve (solid line) of the map 162 is corrected by the
efficiency slope which is defined by the map 163 and the operating
state of the engine 1.
The ECU 10 defines the thermal efficiency at the rich limit based
on the efficiency of MBT and the map 164 determined beforehand. The
map 164 defines a relation of the engine speed, the filling
efficiency, and the thermal efficiency at MBT.
When the thermal efficiency at the rich limit is calculated, the
ECU 10 then calculates the torque corresponding to the thermal
efficiency concerned (i.e., the rich limit torque) based on the
thermal efficiency at the rich limit, a volume per cylinder, and a
calorific value at the rich limit injection amount (a fuel
injection amount in the reduced-cylinder operation during the
change).
Returning to the flowchart of FIG. 14.
The ECU 10 compares the calculated rich limit torque with the
target torque. Then, the ECU 10 determines whether the rich limit
torque is below the target torque (Step S149). As a result, if the
rich limit torque is below the target torque, the preparation
control process returns. The preparation control process repeats
the processing of Steps S141-S149 described above until the rich
limit torque becomes above the target torque. On the other hand, if
the rich limit torque becomes above the target torque, the process
shifts to the reduced-cylinder operation (Step S150).
If the process shifts to the reduced-cylinder operation when the
rich limit torque is below the target torque (i.e., when the target
torque is larger than the rich limit torque), the number of
combustion chambers 17 where combustion is performed decreases, and
the amount of fuel injected into the combustion chambers 17
increases accordingly. Therefore, the A/F becomes relatively rich,
which is a state where raw NO.sub.x may occur.
On the other hand, if the process shifts to the reduced-cylinder
operation when the rich limit torque becomes above the target
torque (i.e., when the target torque is smaller than the rich limit
torque), the degradation of the emission performance can be
prevented because the state where the generation of raw NO.sub.x is
suppressed can be maintained.
Moreover, if the process does not transit to the reduced-cylinder
operation even if the rich limit torque becomes above the target
torque (i.e., even if the rich limit torque exceeds the target
torque), the air-fuel ratio of the mixture gas becomes excessively
lean to cause unstable SPCCI combustion, in some cases, to cause a
misfire (exceeding the lean limit).
The ECU 10 ends the fuel amount maintain processing described above
at the given air-fuel ratio at which the air amount reaches the
given suitable amount (not excessive or insufficient), and starts
the reduced-cylinder operation. That is, by shifting to the
reduced-cylinder operation when the rich limit torque becomes above
the target torque, the change can be achieved in a short period of
time, and the stable SPCCI combustion can be realized even during
the transition period. Therefore, the smooth change can be
performed.
By the transition to the reduced-cylinder operation, the number of
cylinders where SPCCI combustion is performed decreases from four
cylinders to two cylinders, and the ECU 10 changes (increases) the
amount of fuel injected into the combustion chambers 17 where SPCCI
combustion is performed into the target fuel amount of the
reduced-cylinder operation. Moreover, the ECU 10 sets the
reduced-cylinder operation change flag to 0 (Step S151). Therefore,
the change from the all-cylinder operation to the reduced-cylinder
operation is finished.
(Time Chart of First Preparation Control Pattern)
FIG. 17 illustrates one example of a time chart of a pattern of the
first preparation control in which the operation is changed from
the all-cylinder operation to the reduced-cylinder operation. In
the time chart, time progresses from the left to the right. In the
time chart, changes of primary parameters used for the preparation
control are illustrated.
In order to reduce the torque shock throughout a period of the
preparation control, and partial periods adjacent before and after
the preparation control period, the target torque of the engine 1,
i.e., the total amount of fuel supplied to the engine 1 is
maintained constant or substantially constant (refer to 17f). In
the low-load range A1, the engine 1 before the preparation control
is started operates at the given lean air-fuel ratio by SPCCI
combustion of the combustion chambers 17 of all the four cylinders
(refer to 17b and 17e).
When the reduced-cylinder operation change flag is changed to 1 at
a time t11 (refer to 17a), the opening of the throttle valve 43
changes from small to large. If the opening of the throttle valve
43 increases, the amount of air supplied to each combustion chamber
17 increases gradually (refer to 17c).
The amount of fuel injected into each combustion chamber 17 is
maintained at the target fuel amount in the all-cylinder operation
during the change (refer to 17d). Thus, the air-fuel ratio of the
mixture gas of each combustion chamber 17 increases to be gradually
leaner (refer to 17e). Since the air-fuel ratio is leaner than the
lean air-fuel ratio, there is no possibility that raw NO.sub.x
occurs.
However, if the state is maintained as it is, SPCCI combustion
becomes unstable and it will reach a state where misfire may occur
(lean limit), and therefore, it will become impossible to perform
the smooth change.
On the other hand, in this engine 1, the ECU 10 ends the
preparation control at the suitable timing where the generation of
raw NO.sub.x can be suppressed, before reaching the lean limit, and
then changes the operation to the reduced-cylinder operation. That
is, the ECU 10 shifts to the reduced-cylinder operation when the
rich limit torque becomes above the target torque, as described
above. In other words, the ECU 10 (cylinder count control module
10a) ends the fuel amount maintain processing in a given air-fuel
ratio state where the actual air amount which is increasing reaches
the given amount, and then starts the reduced-cylinder operation (a
time t12). At the time t12 when the preparation control ends, the
reduced-cylinder operation change flag is changed to 0 (refer to
17a).
Specifically, the given threshold (rich limit A/F) used as a
reference for suppressing raw NO.sub.x is defined by the imaginary
air-fuel ratio corresponding to the rich limit torque which is the
same value as the target torque. The ECU 10 shifts to the
reduced-cylinder operation when the given air-fuel ratio (rich
air-fuel ratio), which is defined based on the actual air amount
and the amount of fuel injected in the reduced-cylinder operation
during the change, reaches the threshold.
On the other hand, if the operation is changed to the
reduced-cylinder operation at an early timing when the rich limit
torque has not become above the target torque, for example, as
illustrated by a time t13, there is a possibility that raw NO.sub.x
occurs because the rich air-fuel ratio is lower than the threshold,
as illustrated by "Z." Therefore, the degradation of the emission
performance cannot be suppressed.
On the other hand, in this engine 1, since the ECU 10 changes the
operation to the reduced-cylinder operation at the suitable timing
which can suppress the generation of raw NO.sub.x before reaching
the lean limit without excess and insufficiency, the operation can
be changed smoothly, while preventing the degradation of the
emission performance.
At this time, as illustrated, the actual air amount may not have
reached the target air amount, but since the air-fuel ratio then
becomes leaner, there is no possibility that raw NO.sub.x occurs
(refer to 17e). Then, at a time t14, when the actual air amount
reaches the target air amount, the change from the all-cylinder
operation to the reduced-cylinder operation is finished.
(Second Preparation Control Pattern: Change from all-Cylinder
Operation to Reduced-Cylinder Operation)
FIG. 18 illustrates another example of the preparation control to
change the operation from the all-cylinder operation to the
reduced-cylinder operation (a pattern of the second preparation
control). Steps S181-S186 are the same as Steps S141-S147 (except
for Step S143) in the pattern of the first preparation control
described above. Therefore, description of these steps is
omitted.
In this preparation control pattern, the ECU 10 reads the amount of
air actually filled up in the combustion chamber 17 (Step S186),
and then calculates the retard limit torque and the rich limit
torque based on the read actual air amount (Step S187).
The ECU 10 sets the target fuel injection amount of the preparation
control based on the actual air amount (Step S188). The target fuel
injection amount set here is a fuel amount corresponding to the
increase in the actual air amount, in order to maintain the lean
air-fuel ratio (target A/F). The target fuel injection amount is
greater than the injection amount required for the engine 1
outputting the target torque in the all-cylinder operation. That
is, the ECU 10 (cylinder count control module 10a) outputs the
signal to the injector 6 to perform processing in which the amount
of fuel injected into each of the combustion chambers 17 is
increased (the fuel amount increase processing).
Next, the target ignition timing is set based on the target fuel
injection amount setting and the target torque (Step S189). The
target ignition timing set here is retarded so that the increasing
amount of torque due to the increase in the fuel amount is reduced.
That is, the ECU 10 (cylinder count control module 10a) outputs the
signal to the ignition plug 25 to retard the ignition timing (a
retard processing). In SPCCI combustion, by retarding the ignition
timing, the timing of SI combustion is retarded, and the timing at
which CI combustion starts is also retarded. Therefore, the torque
of the engine 1 can be reduced effectively.
Next, the ECU 10 determines whether the calculated retard limit
torque is below the target torque (Step S190). If the retard limit
torque is below the target torque, the amount of fuel to be
injected can be increased by retarding the ignition timing.
Therefore, since the fuel amount can also be increased according to
the increase in the air amount, it can prevent that the air-fuel
ratio becomes lean (the lean air-fuel ratio can be kept). As a
result, the stable SPCCI combustion can be realized.
If the retard limit torque is below the target torque, the ECU 10
causes the injector 6 to inject the fuel according to the target
injection amount, and then causes the ignition plug 25 to ignite
the fuel according to the target ignition timing setting (Steps
S192 and S193).
On the other hand, if the retard limit torque exceeds the target
torque, the ignition timing cannot be retarded any more.
Thus, the ECU 10 (cylinder count control module 10a) performs a
processing to restrict the ignition timing below the retarding
amount at that time, after the retard processing reaches the limit
(a restricted retard processing).
If the amount of fuel to be injected is increased while the
retarding of ignition timing is restricted, the torque outputted
from the engine 1 also increases and the torque shock occurs. In
order to reduce the torque shock, if the increase in the amount of
fuel to be injected is also restricted, there is a possibility that
the air-fuel ratio of the mixture gas becomes lean and SPCCI
combustion becomes unstable.
Therefore, in such a case, it is desirable that the ECU 10
(cylinder count control module 10a) performs a processing to divert
a part of the torque outputted from the engine 1 (a load adjustment
processing), while performing the restricted retard processing
(Step S191).
For example, the ECU 10 may output a signal to the alternator 57
which is an auxiliary machinery to increase the load. Thus, it
becomes possible to continue the increase in the amount of fuel to
be injected, while suppressing the generation of the torque shock.
As a result, even after the retard processing reaches the limit, it
can prevent that the air-fuel ratio becomes lean (the lean air-fuel
ratio can be kept). As a result, the stable SPCCI combustion can
continuously be realized. Note that unless the lean limit is
reached, the retard processing or the restricted retard processing
may be continued, while permitting that the air-fuel ratio becomes
lean.
Next, the ECU 10 compares the calculated rich limit torque with the
target torque. Then, the ECU 10 determines whether the rich limit
torque is below the target torque (Step S194). As a result, if the
rich limit torque is below the target torque, the preparation
control process returns. The preparation control process repeats
the processings at Steps S181-S194 described above until the rich
limit torque becomes above the target torque.
On the other hand, when the rich limit torque becomes above the
target torque, the process shifts to the reduced-cylinder operation
(Step S195). That is, the ECU 10 ends the fuel amount increase
processing and the retard processing (or the restricted retard
processing) described above at the given air-fuel ratio where the
air amount reaches the given amount without excess and
insufficiency, and then starts the reduced-cylinder operation.
By the transition to the reduced-cylinder operation, the number of
cylinders where SPCCI combustion is performed decreases from four
cylinders to two cylinders, and the ECU 10 changes (increases) the
amount of fuel injected into the combustion chambers where SPCCI
combustion is performed to the target fuel amount of the
reduced-cylinder operation. Since the air amount and the fuel
amount during the change are close to the target air amount and the
target fuel amount of the reduced-cylinder operation, compared with
the first preparation control pattern, the change in the state at
the startup of the reduced-cylinder operation is small and, thus,
the operation can be changed smoothly. Moreover, the ECU 10 sets
the reduced-cylinder operation change flag to 0 (Step S196). Thus,
the change from the all-cylinder operation to the reduced-cylinder
operation is finished.
(Time Chart of Second Preparation Control Pattern)
FIG. 19 illustrates one example of a time chart of the second
preparation control pattern in which the operation is changed from
the all-cylinder operation to the reduced-cylinder operation,
similar to FIG. 17.
Here, the ignition retarding amount means a retarding amount from
the ignition timing based on the normal engine control. Note that
since the speed of SI combustion becomes slower when the air-fuel
ratio becomes lean, the normal ignition timing is controlled to be
advanced accordingly.
Since the torque shock is reduced throughout the preparation
control period and the partial periods adjacent before and after to
the preparation control period, the target torque of the engine 1,
i.e., the total amount of fuel supplied to the engine 1 is
maintained constant or substantially constant (refer to 19h). In
the low-load range, the engine 1 before the preparation control is
started is operated by SPCCI combustion with the combustion
chambers 17 of all the four cylinders at the given lean air-fuel
ratio (refer to 19b and 19e).
When the reduced-cylinder operation change flag is changed to 1 at
a time t21 (refer to 19a), the opening of the throttle valve 43
changes from small to large, and the amount of air supplied to each
combustion chamber 17 increases gradually (refer to 19c).
The amount of fuel injected into each combustion chamber 17 is
increased according to the actual air amount so that the air-fuel
ratio is maintained at the lean air-fuel ratio (refer to 19d). In
order to maintain the target torque, the ignition timing is
retarded according to the increase in the fuel amount (refer to
19f). The retarding amount increases as the air amount and the fuel
amount increase.
In the illustrated preparation control pattern, the target torque
exceeds the retard limit torque at a time t22. That is, the
ignition retarding amount reaches the retard limit (refer to 19f).
Since the ignition timing cannot be retarded any more, the ECU 10
maintains the retarding amount of the ignition timing. Thus, the
stability of SPCCI combustion is secured.
In order to continue the increase in the injecting fuel amount, the
ECU 10 executes the load adjustment processing in which the load of
alternator 57 is increased, in addition to such a restricted retard
processing (refer to 19g). As a result, the increase in the
injecting fuel amount can be continued, while maintaining the
air-fuel ratio at the lean air-fuel ratio, thereby keeping the
torque constant.
Then, at a time t23, when the rich limit torque becomes above the
target torque (when the imaginary rich air-fuel ratio reaches the
given threshold), the fuel amount increase processing and the
retard processing (restricted retard processing) which are
described above are ended, and the reduced-cylinder operation is
then started. At the time t23 when the preparation control ends,
the reduced-cylinder operation change flag is changed to 0 (refer
to 19a). Then, at a time t24, when the actual air amount reaches
the target air amount, the change from the all-cylinder operation
to the reduced-cylinder operation is finished.
(Third Preparation Control Pattern: Change from Reduced-Cylinder
Operation to all-Cylinder Operation)
FIG. 20 illustrates one example of the preparation control to
change the operation from the reduced-cylinder operation to the
all-cylinder operation (pattern of a third preparation
control).
The third preparation control pattern is substantially the same as
the first preparation control pattern, and only the difference is
that the operating condition in question is interchanged between
the all-cylinder operation and the reduced-cylinder operation. That
is, Steps S141-S151 in FIG. 14 corresponds to Steps S201-S211 in
FIG. 20, respectively. In addition, the increase/decrease in the
fuel amount and the air amount, and the processings accompanying
the increase/decrease are also reversed. Therefore, description
thereof is omitted, and only the different contents are described
with the following time chart.
(Time Chart of Third Preparation Control Pattern)
FIG. 21 illustrates one example of a time chart of the third
preparation control pattern to change the operation from the
reduced-cylinder operation to the all-cylinder operation, similar
to FIG. 17.
In order to reduce the torque shock throughout the preparation
control period, and the partial periods adjacent before and after
the preparation control period, the target torque of the engine 1,
i.e., the total amount of fuel supplied to the engine 1 is
maintained constant or substantially constant (refer to 21f). In
the low-load range, the engine 1 before the preparation control is
started operates by SPCCI combustion with the combustion chambers
17 of two cylinders at the given lean air-fuel ratio (refer to 21b
and 21e).
When the all-cylinder operation change flag is changed to 1 at a
time t31 (refer to 21a), the opening of the throttle valve 43
changes from large to small, and the amount of air supplied to each
combustion chamber 17 decreases gradually (refer to 21c).
The amount of fuel injected into the combustion chambers 17 of two
cylinders is maintained at the target fuel amount of the
reduced-cylinder operation during the change (refer to 21d). Thus,
the air-fuel ratio in the combustion chambers 17 where SPCCI
combustion is performed decreases, and becomes gradually richer
(refer to 21e).
Therefore, if this continues as it is, the possibility that raw
NO.sub.x occurs arises.
On the other hand, in this engine 1, the ECU 10 ends the
preparation control at a suitable timing before raw NO.sub.x may be
generated, and then changes the operation to the all-cylinder
operation. That is, the ECU 10 shifts to the all-cylinder
operation, when the rich limit torque becomes above the target
torque, as described above. In other words, the ECU 10 (cylinder
count control module 10a) ends the fuel amount maintain processing
at the given air-fuel ratio where the actual air amount which is
decreasing reaches the given amount, and then starts the
all-cylinder operation (time t32).
Since the amount of fuel injected to the combustion chambers 17
where SPCCI combustion is performed in the reduced-cylinder
operation decreases by changing to the all-cylinder operation, the
air-fuel ratio becomes lean. Therefore, the generation of raw
NO.sub.x is suppressed. Since the operation is changed smoothly at
the early timing without excess and insufficiency, the stable
change can be performed. At the time t32 where the preparation
control ends, the all-cylinder operation change flag is changed to
0 (refer to 21a).
At this time, as illustrated, the actual air amount may not have
reached the target air amount, but since the air-fuel ratio then
becomes leaner, there is no possibility that raw NO.sub.x occurs
(refer to 21e). Then, at a time t33, when the actual air amount
reaches the target air amount, the change from the reduced-cylinder
operation to the all-cylinder operation is finished.
OTHER EMBODIMENTS
Note that the technology disclosed herein is not limited to be
applied to the engine 1 of the configuration described above. The
engine 1 may adopt various configurations.
It should be understood that the embodiments herein are
illustrative and not restrictive, since the scope of the invention
is defined by the appended claims rather than by the description
preceding them, and all changes that fall within metes and bounds
of the claims, or equivalence of such metes and bounds thereof, are
therefore intended to be embraced by the claims.
DESCRIPTION OF REFERENCE CHARACTERS
1 Engine 10 ECU (Control Device) 10a Cylinder Count Control Module
17 Combustion Chamber 25 Ignition Plug 3 Piston 43 Throttle Valve
(Air Adjusting Part) 57 Alternator 6 Injector (Fuel Injection
Valve)
* * * * *